An Analysis of Pesticide Use in California 1991 - 1995

Larry Wilhoit1, David Supkoff1, John Steggall1, Adolf Braun1,

Charlie Goodman2, Bob Hobza1, Barbara Todd2, Marshall Lee1

1 Department of Pesticide Regulation, Environmental Monitoring and Pest
Management Branch, 1020 N Street, Sacramento, California 95814-5624

2 California Department of Food and Agriculture, Office of Pesticide
Consultation and Analysis, 1220 N Street, Sacramento, California 95814



California State Seal

December 1998 STATE OF CALIFORNIA
Environmental Protection Agency
Department of Pesticide Regulation
Environmental Monitoring and Pest Management Branch
Pest Management Analysis and Planning Program
Sacramento, California 95814-5624

PM 98 - 01


Abstract

In 1990, the Department of Pesticide Regulation began requiring all agricultural pesticide use to be reported. This replaced a system of limited use reporting. Under the new system, the Department required farmers and other users of agricultural pesticides to submit complete, site-specific documentation of every pesticide application.

For this analysis, several types of queries were run on the Pesticide Use Reporting (PUR) data. Analyses were calculated for total pounds, number of applications and acres treated of all active ingredients on all agricultural crops. Total pounds, number of applications, and acres treated were run for each active ingredient separately. In addition, the 20 pesticides with the highest increase in pounds used from 1991 to 1995 were determined, and for the same period, the 10 pesticides that had the highest decrease in pound used. Because numerical computations cannot explain the reasons for trends in pesticide use, scientists from DPR's Environmental Monitoring and Pest Management Branch also interviewed university specialists and farm advisors to determine the reasons for the changes.

The increase in pounds of pesticide used from 1991 to 1995 was due mostly to a few situations. In many crops, use of many pesticides decreased. DPR's analysis found that six pesticides (sulfur, metam-sodium, oils, methyl bromide, copper sulfate, and chlorpyrifos) accounted for 41 million pounds out of the 56 million pound increase of all agricultural pesticides. Most of the use of these six pesticides was on just a few crops. The use of these six pesticides increased for reasons that fall into four main categories: (1) an increase in acres grown; (2) greater pest problems; (3) lack of other ways to control a pest; and (4) decisions to use reduced risk pesticides. The lack of alternatives arose either because alternative pesticides were (1) suspended or canceled or (2) losing effectiveness because of resistance.

Table of Contents

Table of Contents Page Number
Abstract I
 
Table of contents i
     List of Tables ii
     List of Figures iii
 
Introduction 1
Analyzing the use report data 1
Evaluation methods 2
Increases in use of certain categories of materials 4
     Probable carcinogens 4
     Category II organophosphates and carbamates 5
     Restricted use materials 5
 
Patterns of pesticide use 5
     Sulfur 6
          Grapes 6
          Tomatoes 7
     Metam-sodium 7
          Carrots 7
          Tomatoes 8
          Cotton 8
          Potatoes 9
     Oils 9
          Oranges and lemons 9
          Cotton, prune, olive, cherry 10
     Methyl bromide 10
          Uncultivated agriculture 11
          Head lettuce 11
          Wine grapes 11
     Copper sulfate (pentahydrate) 12
          Rice 12
     Chlorpyrifos 13
          Cotton 13
 
Conclusion and discussion 14
 
Appendix 25


List of Tables

Table 1. Pounds of 50 active ingredients used in California agriculture
Appendix Table 1. Pounds of each active ingredients used in California agriculture
Appendix Table 2. Number of applications of each active ingredients used in California agriculture
Appendix Table 3. Acres treated by each active ingredients used in California agriculture


List of Figures

Figure 1. Changes in agricultural pesticide use from 1991 through 1995
Figure 2. Pounds of active ingredients whose use has increased the most from 1991 to 1995
Figure 3. Pounds of sulfur used on the major crops
Figure 4. Pounds of metam-sodium used on the major crops
Figure 5. Pounds of oil used on the major crops
Figure 6. Pounds of methyl bromide used on the major crops
Figure 7. Pounds of copper sulfate used on the major crops
Figure 8. Pounds of chlorpyrifos used on the major crops


Introduction

In 1990, the Department of Pesticide Regulation (DPR) began requiring all agricultural pesticide use to be reported. This replaced a system of limited use reporting. Under the new system, the Department required farmers and other users of agricultural pesticides to submit complete, site-specific documentation of every pesticide application. These reporting requirements also were extended to pesticides used on parks, golf courses, cemeteries, rangeland and pastures, and along roadside and railroad rights-of-way. All reports of pesticide use include: the date of application; where the treatment occurred; the applicator, the pesticide; and the amount applied. In addition, businesses that apply pesticides in buildings are also required to report.

An enormous amount of data is collected under the new reporting system. Each year, more than two million use report records are submitted to the County Agricultural Commissioners and then transferred to the Department. Each record contains more than 30 separate pieces of information. California was the first state to set up a full pesticide use reporting program, and establishing an accurate and comprehensive mechanism for collecting the data was the Department's priority. Among other things, the Department developed computer application programs to help counties manage their data collection tasks, and software that allows counties and pesticide users to submit reports electronically.

Analyzing the Use Report Data

In 1996, with five years of use reporting history in hand, Department scientists began developing methods to analyze the data and to check it for entry errors. Critical to this process were advances in computer technology, primarily the increasing availability to the Department of powerful computer workstations and relational database software that can handle large amounts of data with flexibility and speed.

In September 1997, a group called Californians for Pesticide Reform (CPR) published an analysis of pesticide use in California. Its publication, entitled Rising Toxic Tide: Pesticide Use in California, 1991 - 1995, [Rising] interpreted data from the Department's pesticide use reporting program. It states that the reported use of all pesticides in California increased 31 percent from 1991 to 1995, and that pesticide use in production agriculture has increased 37 percent during this period. Further, the author states that use of the most toxic pesticides has increased. The use of probable carcinogens increased 129 percent, use of category II organophosphates and carbamates (what Rising referred to as "nerve toxins") increased 52 percent, and use of restricted use pesticides increased 34 percent. The author also states that this increase is not due to increased planted acreage but to increased intensity of use.

To respond to the report and its conclusions adequately, DPR scientists examined the findings and extended the analysis to gain a more accurate understanding of the trends in pesticide use on the major crops. The Department's priority was to analyze the use report database in a way that provided meaningful conclusions relevant to the regulation of pesticides in California. For that reason, scientists in the Department’s Environmental Monitoring and Pest Management Branch conducted a far more extensive and in-depth analysis of the pesticide use data than found in Rising. As part of this effort, the Department examined the same data set as Rising, not only to provide points of comparison and but also to ensure that significant trends in pesticide use were not overlooked.

Evaluation methods

All analyses of pesticide use were done by running queries on DPR’s pesticide use reporting database (PUR). The PUR contains information on nearly all agricultural crop pesticide use. Pesticide use on livestock is not required to be reported. Nonagricultural reporting is limited to commercial applicators. Therefore, most analyses in this report focus on crop agricultural uses. The only exception is the analysis of chemical use based on various toxicological classifications (e.g., use of probable carcinogens); these analyses are of all uses reported in the PUR.

Crop acreage for 1991 through 1995 is from the 1996 California Agricultural Resource Directory, published by the California Department of Food and Agriculture. Harvested acres (rather than planted acres) were used for field and vegetable crops and both bearing and nonbearing acres were summed for fruit and nut crops.

Pesticide use can be measured in many different ways including (1) number of pounds of active ingredient, (2) number of pesticide applications, and (3) total number of acres treated. The "active ingredient" is the component in the pesticide product that kills or otherwise controls the target pest. Number of acres treated could mean either the cumulative number of acres treated, in which the acres treated in each application is summed even when the same field is sprayed more than once in a year, or the base number of acres treated, in which each acre treated is counted only once. In this report only cumulative acres treated are used.

Most of the analyses in this report use the number of pounds of pesticide active ingredient. When total pounds of the same active ingredient applied to different crops are compared, a reasonable contrast can be measured. However, different pesticides vary tremendously in weight and application rates, making comparisons of the aggregate weights of multiple pesticides problematic. For example, an increase in pounds of pesticide used could result from the replacement of lighter materials with heavier materials, or replacement of a more toxic chemical requiring a single use each season with a reduced-risk compound requiring multiple applications. When either of these is the case, it is misleading to say pesticide use increased. The other two measures of pesticide use (number of applications and sum of acres treated) can be compared for different active ingredients.

For this analysis, several types of queries were run on the PUR data. Analyses were run for total pounds, number of applications and acres treated of all active ingredients on all agricultural crops. Total pounds, number of applications, and acres treated were run for each active ingredient separately. In addition, the 20 pesticides with the highest increase in pounds used from 1991 to 1995 were determined, and for the same period, the 10 pesticides that had the highest decrease in pounds used. The total pounds, number of applications, and acres treated for these 30 chemicals were also run.

The results of some of these queries are given in the tables in the appendix. In this report, only a few of the pesticides and crops with the largest increases are discussed.

To improve data quality, records considered probable errors (outliers) were removed from the PUR database. (Errors can occur, for example, when those reporting pesticide use shift decimal points during data entry.) Rates were considered probable errors if they were higher than 200 pounds per acre (or greater than 1000 pounds per acre for fumigants); if they were 50 times larger than the median rate for all uses with the same pesticide product, crop treated, and unit treated; and if they were higher than a value determined by a neural network procedure that approximates what a group of 12 scientists believed were obvious outliers. Although these criteria removed only about 1 percent of PUR records, some records had such extremely high values that they significantly affected total pounds applied of some pesticides. For example, in the 1995 database, there is an erroneous record of a carbaryl application of 596,511 pounds to five acres of oranges. (The median rate of carbaryl use on oranges in 1995 was 12 pounds per acre).

A few other special problems appeared during the analysis. The PUR contains two categories for tomatoes, "tomato" and "tomato, processing." The implication is that the "tomato" category includes just fresh market tomatoes. However, in the first years of full use reporting, the use of pesticides reported on processing tomatoes was extremely low and the use on just tomatoes was extremely high. This pattern was reversed in the later years. However, according to the CDFA crop statistics, the proportion of fresh market tomatoes remained at close to 12 percent of the total tomato acreage each year. Thus, it appears that in the earlier years (when farmers were still becoming familiar with the use reporting system), many growers recorded applications to processing tomatoes in the "tomato" category. As a way to avoid this confusion, in this report both tomato categories were combined.

Also, the classification of the different kinds of oils appeared to be inconsistently used in the PUR. There are several oil active ingredients listed in the PUR (mineral oil, petroleum oil, petroleum distillates, and petroleum hydrocarbons) but they are only vaguely defined. Different growers using the same oil product apparently report it as different active ingredients. For the purposes of pest management there is little or no difference in use between these types of oils. Thus, this analysis combines all oils into a single pesticide category.

Finally, to get a better understanding of the causes of the increases, DPR scientists interviewed several farm advisors and IPM specialists.

Increases in use of certain categories of materials

As part of its analysis, the Department examined the same data set as Rising, not only to provide points of comparison and but also to ensure that significant trends in pesticide use were not overlooked. Rising grouped pesticides by toxicological category (probable carcinogens, category II organophosphates and carbamates, and restricted use materials) and graphed their use for the years 1991 through 1995. Compounds were categorized into these respective groups depending on whether they were found on various U.S. Environmental Protection Agency, DPR, or Proposition 65 lists. Rising concluded from these data that use of the most toxic pesticides had risen between 1991 and 1995.

To examine the summary statistics presented in the Rising report, DPR carried out a parallel analysis based on all uses reported in the PUR (not just agricultural uses). Statistical regression analysis can be used to determine trends. Although the Department has an accurate measure of pesticide use in each year (and therefore does need to use a sample to get the value because it has the entire population), a statistical analysis is needed to determine if a real trend has occurred. The pounds used varies from year to year because of many random factors (such as weather, pest populations, prices). For example, although pesticide use was higher in 1995 than in 1991, without a statistical analysis one cannot know whether this difference was due to a general year-to-year trend or whether it was just due to the normal yearly random variation in use.

Probable Carcinogens

This category showed an apparently linear increase from about 10 million to 23 million pounds between 1991 and 1995 (r = 0.98, P < 0.01). However, the greatest proportion of this increase, more than ten million pounds or 79 percent, was due to increased use of a single active ingredient--metam-sodium. If metam-sodium is removed from the data, the use of probable carcinogens increased from approximately 5 million pounds to 8 million pounds, but is still linearly correlated with year (r = 0.98, P < 0.01). That is, there is a statistically significant increasing use in probable carcinogens in the period from 1991 to 1995. After metam-sodium, seven pesticides (1,3-dichloropropene, captan, chlorothalonil, creosote, mancozeb, maneb, and propargite), ranked according to their absolute increase between 1991 and 1995, contributed the remaining increase of 3 million pounds. There is a nonsignificant correlation between pounds applied and year after these eight materials are subtracted from the list (r = -0.72, P > 0.1). Thus, nearly all of the increase in probable carcinogens was due to eight pesticides, with metam-sodium having the greatest increase.

Category II organophosphates and carbamates

Two large errors in the 1995 PUR contributed to the increase in category II organophosphates and carbamates presented in the graph on page 6 of Rising. One error was a reported application of 1,147,308 pounds of diazinon on a structural site and the other was a reported application of 596,511 pounds of carbaryl on five acres of oranges. These were errors made by the counties in entering the amount of pesticides used. They have since been corrected in our database but this had not yet been done when the authors of Rising requested the PUR data (although they were informed of the likelihood of a entry errors in the database).

After removing these two errors, the use of category II organophosphates and carbamates rose from 5.6 million pounds to 6.8 million pounds. The correlation coefficient is close to significance (r = 0.87, p ~ 0.05) but since the data is clearly not linear, it is questionable whether analyzing it in such a fashion is reasonable. Nearly the entire increase in category II organophosphates and carbamates is due to a single active ingredient--chlorpyrifos. When chlorpyrifos data is subtracted from the total, there is no apparent trend--the total varies each year in a narrow range, between 3.5 million and 3.2 million pounds.

Restricted use materials

Restricted use materials do not show a statistically significant linear increase (from 36 million pounds to 48 million pounds) between 1991 and 1995 (r = 0.84, P = 0.07). However, the sample size is small and shows potential non-linearity. As in the probable carcinogen group, metam-sodium also accounts for a substantial portion of the absolute increase (10.2 million of the 12 million pound increase). When metam-sodium is subtracted from the total, there is no apparent increase in the remaining restricted materials (r = 0.21, P > 0.05).

Patterns of pesticide use

The total pounds of pesticides applied, the number of applications, and the cumulative number of acres treated increased from 1991 to 1995. However, summing over all pesticides and all crops does not reveal a complete story. For example, the increase in pesticide use does not necessarily mean that adoption of IPM is decreasing. Pesticide use depends on many factors. Weather plays a significant role--wet weather, for example, encourages weed growth and humid weather promotes some types of disease. Changes in pest population can affect pesticide use, as can changes in pest biology. A significant infestation may overwhelm natural enemies that may be present. And the development of resistance to certain chemical tools can lead to an increase in use of alternatives. Pesticide use also depends on the crop grown. Less pesticide, a costly input, is used on low-value crops; more pesticides are used on crops with a low threshold of damage, such as lettuce. The type of crop planted also ties back to the weather, since in a drought, farmers are less likely to plant crops that require large quantities of water.

The conclusion is that one cannot simply examine aggregate totals and gain an accurate understanding of pesticide use in California. To discern what is happening in pest management in California agriculture, closer analysis of the use of particular pesticides on individual crops is needed.

DPR’s analysis revealed that six pesticides had the largest absolute increase in pounds used: sulfur, metam-sodium, oils, methyl bromide, copper sulfate (pentahydrate), and chlorpyrifos (Table 1 and Figure 2). The uses and explanation of increases in use will be examined for the major crops for each of these pesticides.

Sulfur

Sulfur is a naturally occurring element widely used as a fungicide in both conventional and organic farming. From 1991 to 1995, it had the highest use in pounds applied and the largest increase in pounds used (Table 1). It also had the highest use and greatest increase in number of applications and acres treated (Appendix Tables 1 - 3). Most of the use of sulfur (and increase in use) has been on grapes and tomatoes (Figure 3). The category "grapes" includes primarily table and raisin grapes. (Although there is a separate use reporting category for wine grapes, some counties report pesticide use on wine grapes in the nonspecific "grape" category.) In this report, the category "tomatoes" includes both fresh market and processing tomatoes.

Tomato acreage was similar in 1991 and 1995. While there was an increase in wine grape acreage of 10 percent between 1991 and 1995, this increase is smaller than the 72 percent increase in sulfur use on wines.

Grapes: Sulfur controls powdery mildew on wine, raisin and table grapes and has been increasingly used for resistance management.

According to Cooperative Extension farm advisors and a UC Davis plant pathologist, after Bayleton (triadimefon), a dimethylation inhibitor (DMI), was introduced in the mid-1980’s, sulfur use declined. Later, when powdery mildew resistance to DMI’s developed, sulfur applications again increased. Resistance to other DMI’s (in particular myclobutanil and fenarimol) further spurred sulfur usage. Raisin growers rely almost exclusively on sulfur; wine and table grape growers employ both sulfur and DMI’s.

Sulfur is approved for use in organic wine grape production and DMI’s are not. More growers are switching to organic wine grapes and to sulfur for powdery mildew control. Thus, resistance management and switch to organic production seem to be the driving forces for increased sulfur use.

Tomatoes: Sulfur is used primarily for control of powdery mildew and russet mites on tomatoes.

One pest management expert interviewed suggested that the increase in the use of sulfur on tomatoes, especially from 1993 through 1995, might be explained by a combination of increased powdery mildew, russet mite pressure, spring rains, and a transition from furrow to sprinkler irrigation to conserve water. All these factors can increase plant disease, thereby requiring increased fungicide use. However, several other experts interviewed could not explain the increase in use of sulfur on tomatoes.

Metam-sodium

The fumigant metam-sodium had the next highest increase in pounds applied (Table 1). However, because metam-sodium is used at higher poundage rates than most pesticides, apparent use is exaggerated if the only indicator is pounds applied. For example, metam-sodium was applied at the median rate of 89.5 pounds per acre in 1995 while most pesticides are applied at rates of around 1 or 2 pounds per acre. Some pesticides are applied at much lower rates. For example, avermectin was applied at a median rate 0.0095 pounds per acre. The total number of pounds applied in 1995 with metam-sodium was 15,075,863 and with avermectin 6,924. From these numbers it would seem that metam-sodium use was much higher (2,177 times higher) than that of avermectin. However, the number of applications of metam-sodium was 4,648 but for avermectin was 27,190. From these numbers it would seem avermectin use was higher. The point is that there are different measures of "use" which can give very different results.

The crops that had the greatest increase in metam-sodium use were carrots, tomatoes, cotton, potatoes, and soil application to outdoor pre-planted seed beds (Figure 4). Metam-sodium is usually applied to the soil before planting. Of these crops, only cotton had a significant increase in acreage (23 percent), but not enough to explain the increase (418 percent) in metam-sodium use.

Carrots: Root-knot nematode is the major pest in all carrot-growing areas of California. The same sandy loam soils that are ideal for carrot production are ideal for the root-knot nematode. Besides causing stubbing and forking, nematodes cause numerous galls on the taproot and feeder roots. The galling and dieback make these carrots unmarketable. Stubby root nematodes and the needle nematode are also responsible for forking and stubbing of roots. Pythium spp. and Rhizoctonia solani are the most common soil-borne fungi that infect carrots.

Before 1990, plant pathogenic nematodes were controlled by 1,3-dichloropropene (best-known brand name, Telone II). According to the PUR of 1989[1]there were 2.7 millionpounds of 1,3&dichloropropene used for carrot production.

In April 1990, DPR suspended most permits for the use of 1,3-dichloropropene after monitoring detected levels of health concern in ambient air in Merced County. As a result, the use of 1,3-dichloropropene dropped fourfold from 1989 levels, to 691,573 pounds in 1990.

After the halt in use of 1,3-dichloropropene, metam-sodium use increased dramatically, from 15,345 pounds in 1989 to 1,395,942 pounds in 1991. Metam-sodium, a broad spectrum biocide, probably had replaced the use of 1,3-dichloropropene. In addition, research in the late 1980’s and early 1990’s demonstrated that metam-sodium preplant treatment was highly effective in season-long control of weeds such as nightshade, nutsedge and morning glory. This may have contributed to the increased use of metam-sodium from 1990 through 1995. According to carrot growers interviewed for this analysis, treated carrot acreage increased steadily over this period as farmers learned how better to employ metam-sodium.

Tomatoes: The target pests for metam-sodium in tomatoes are weeds, particularly nightshade, and nematodes in fresh market tomatoes. Nematodes are not a major problem for processing tomatoes, since farmers plant resistant/tolerant nematode varieties. Hand hoeing was a common practice for weed control until metam-sodium was shown to be effective in controlling nightshade in the late 1980’s and early 1990’s. Metam-sodium has now mostly replaced hand hoeing for weed control because it is less expensive.

Cotton: Metam-sodium is primarily used to control weeds in cotton, particularly nightshade. According to experts interviewed for this analysis, nightshade control was done by hand hoeing before 1990. When metam-sodium was shown to control nightshade effectively and more economically, this product replaced hand hoeing. Soil-applied metam-sodium is commonly used on cotton fields in the San Joaquin Valley to control weeds in the seedrow.

A new cotton herbicide (pyrithiobac-sodium, trade name, Staple) was registered in 1996. It is effective against nightshade and other weeds. Staple can also be used at a much lower rate than metam-sodium (ounces vs. gallons per acre). Pest managers told DPR that the preliminary indication is that the sale of metam-sodium for cotton has dropped by 50 percent in 1997.

Potatoes: Metam-sodium is used to control soil-borne diseases, such as stem and stolon canker (Rhizoctonia solani) and powdery scab (Spongospora subterrane), on potatoes. The use of metam-sodium in potato production has the added benefit of providing weed control, particularly nightshade. Metam-sodium is also recommended for the control of powdery scab by the University of California in its IPM guidelines. Finally, metam-sodium may also have some use in controlling nematodes.

Metam-sodium was used for controlling soil-borne diseases after formaldehyde was canceled for this use in 1990. In addition, metam-sodium was sometimes used for nematode control after the suspension of 1,3-dichloropropene (although ethoprop was a more common alternative). Some of those interviewed suggested that the significant increase of metam-sodium use from 1994 to 1995 may have been due to the serious potato late blight outbreak in 1995. Some weeds, including nightshade, are good hosts and are an inoculum source for this disease if not controlled.

Oils

Oils had the third highest increase from 1991 to 1995 in pounds applied (Table 1). Oils are increasingly being used because of their low toxicity to humans and beneficial organisms. The crops that saw the greatest increase were orange, lemon, cotton, and prunes (Figure 5). Again, only cotton had an increase in planted acreage (23 percent) but not enough to account for the increase in oil use (300 percent) for this crop.

Oranges and lemons: In citrus, oils are primarily used for the control of scale and mite pests and, to a lesser extent, other pest insects. Chlorobenzilate, which was used for bud mite control, was withdrawn and oil has become the major alternative. Resistance of citrus red mite to non-oil acaricides and California red and yellow scales to organophosphates and carbamates is increasing and may also be responsible for some increase in oil use. Despite extreme resistance problems to carbamates and organophosphates, many citrus growers continue to use them, but to supplement their efficacy, have increased oil concentrations in sprays. Resistance problems have also driven increases in biologically based IPM programs over the past five years.

Many growers are probably switching to more oil use because it is a reduced risk material and because it plays an important role in IPM programs in citrus. Naturally occurring parasitoids and predators play a crucial role in managing scale and mite pests. In addition, many growers are now trying to use Aphytis and other parasitoids in augmentative release programs. Over use of broad spectrum pesticides will kill these natural enemies and actually disrupt control of scales and mites. However, if natural enemies cannot keep up with pest population growth, limited use of some pesticide may be need. Thus it is important to use pesticides, such as oils, that are less harmful to natural enemies.

Cotton, prune, olive, cherry: Oil is used primarily to control mites on cotton, prune, olive and cherry, but oils can also be used to control other insects. Oil use on these crops has increased because of its low toxicity and because of resistance development in mites to older acaricides, and because of difficulties associated with the remaining acaricides (e.g., propargite has a long period between application and when workers can reenter the field).

Oils are being used to increase the efficacy of newer acaricides. There is also some evidence that resistance problems with some newer acaricides are driving both increasing oil and acaricide use. Finally, using higher rates of oils may enable growers to meet the strict cosmetic standards required by the export market.

Conventionally, dormant sprays have contained mixtures of oil and various organophosphate pesticides, (e.g., diazinon, methomyl, and chlorpyrifos). Insect resistance to these materials has prompted growers to increase the use of oils to supplement their dormant sprays. Farm advisors and UC IPM specialists speculated that severe resistance problems will cause growers to increase oil use to a level just below phytotoxicity, at least until new products are on the market. Some growers have shifted to synthetic pyrethroids (e.g., esfenvalerate and permethrin) in their dormant sprays to replace failing organophosphates and carbamates. Unfortunately, the synthetic pyrethroids break down more slowly and often kill beneficial insects and mites later in the season. A shift toward synthetic pyrethroids may also be a factor explaining increased acaricide and oil use as pyrethroids are often associated with mite and aphid problems later in the season.

As with citrus, use of oils is also probably increasing in these other crops because of their importance in IPM systems.

Methyl bromide

The fumigant methyl bromide had the fourth highest increase in pounds applied (Table 1). Like metam-sodium, methyl bromide is a case where use is exaggerated using pounds applied because it is used at very high rates. The median rate of use of methyl bromide in 1995 was 225 pounds per acre, even higher than that of metam-sodium.

The crops (or sites) which had the greatest increase in methyl bromide use were uncultivated agricultural land, head lettuce, wine grapes, almonds, and soil applications (Figure 6).

Head lettuce acreage did not increase. Wine grape and almond acreage did increase (wine grapes by 10 percent and almonds by 6 percent), though not enough to explain the increase in methyl bromide use (107 percent on wine grapes and 105 percent on almonds).

Uncultivated agriculture: According to the EPA list of site codes, "uncultivated agriculture" includes farm roads, farm walks, farm yards, farm fuel storage areas, non-crop agricultural areas, fencerows (ag), rights-of-way (ag), hedgerows (ag), fallow or idle land including turn-rows, headlands of fields, meadows, soil bank land, summer fallow land, abandoned fields, cropland borders, cropland (fallow), barrier strips, soil bank land (ungrazed).

Methyl bromide is typically applied to soil before planting and growers may indicate what crop is to be planted--lettuce or grapes, for example--or may simply report application to uncultivated land.

Because of its nonspecific nature, explaining changes in use in this reporting category is difficult.

Head lettuce: Methyl bromide may be used to control soil-borne plant pathogens (such as corky root and sclerotinia drop), nematodes, and weeds in head lettuce. PUR data shows that statewide use of methyl bromide on head lettuce increased about 220 percent between 1994 and 1995. In Monterey County, one of the primary head lettuce-producing counties, methyl bromide use on head lettuce increased 436 percent. However, it is important to keep in perspective that although use of methyl bromide increased, it is applied to only a small percentage of head lettuce acreage. Only about 1.5% of the head lettuce acreage was treated with methyl bromide in 1995, up from about 0.7% in the previous years.

The reasons for the increase in the use of methyl bromide appear to be complex and multifaceted. Likely factors (in no particular order) include loss 1,3-dichloropropene, of variability of pest pressures from soil-borne pathogens, the nature of the cropping patterns in the Salinas Valley (two lettuce crops and one cole crop each year on the same parcel of land), and the recognition by growers of the benefits of the methyl bromide/chloropicrin combination. In addition, many growers in the Salinas Valley may have responded to flooding in 1995 and potential subsequent disease pressure by treating with methyl bromide.

Wine grapes: The limiting factor in wine grape production is the replant problem, a complex disorder that is still not clearly understood. It is probably due to a combination of a number of pests such as phylloxera, nematodes, and soil-borne plant pathogens. Grape growers routinely fumigate soil with methyl bromide before planting to improve plant growth in the early years. Soil fumigation with methyl bromide at replanting commonly returns the cost of the treatment, usually with 10 to 50 percent greater initial plant growth, leading to larger, more productive plants when they begin to bear three to seven years after planting.

A large part of the increase in methyl bromide use in wine grapes was due to an increase in the number of vineyard replantings. Though total wine grape acreage increased only 10 percent between 1991 and 1995, nonbearing acres increased 67 percent. Replanting of vineyards is required to replace vines susceptible to phylloxera with resistant varieties. In the planting boom from 1960 to 1980, 60 to 70 percent of Napa and Sonoma vineyards were planted to the now phylloxera-susceptible AxR#1 variety. In Napa and Sonoma counties, virtually all AxR#1 vineyards must be replanted and this process is well underway.

Copper sulfate (pentahydrate)

The insecticide copper sulfate had the fifth highest increase in pounds applied (Table 1). Copper sulfate is used at high rates, so its relative use is exaggerated by simply analyzing pounds applied. Its median rate of use in 1995 was 9.9 pounds per acre, not nearly as much as metam-sodium or methyl bromide, but still more than most pesticides. Nearly all copper sulfate use was on rice (90 percent in 1995) (Figure 7). Although there was a 33 percent increase in rice acreage, the increase in copper sulfate use on rice was even larger (78 percent increase).

Rice: Copper sulfate is used in rice primarily to control tadpole shrimp (Triops longicaudatus), a pest of seedling rice. Treatment is shortly after rice fields are seeded, when foraging activity of newly hatched tadpole shrimp is evident. Applications are aerially at rates ranging from 5 to 10 pounds per acre. Currently, methyl parathion may also be used to control tadpole shrimp. It is also applied aerially, at a rate of 1.25 pounds per acre. Cultural techniques can also be effective against tadpole shrimp. If fields can be flooded quickly and uniformly and if rice is planted immediately after flooding, the rice seedlings may outgrow developing tadpole shrimp. However, if all of these elements are not met, tadpole shrimp may be large enough to cause significant damage if not controlled with copper sulfate or methyl parathion. Copper sulfate also may occasionally be used to control algae in rice fields when algal mats are so dense they retard growth of rice seedlings.

The ratio of rice fields treated with copper sulfate to those treated with methyl parathion increased over the last 15 years. In 1980, there were 16,881 acres of rice treated with copper sulfate, 101,176 with methyl parathion. In 1995, the ratio was reversed with 221,507 acres treated with copper sulfate and 40,249 with methyl parathion. The reasons for the trend away from the use of methyl parathion and toward the use of copper sulfate are reluctance of applicators to handle highly toxic pesticides and reports that tadpole shrimp were becoming resistant to methyl parathion.

The increase in copper sulfate use over methyl parathion is a good example of how looking only at pounds (as Rising does) can distort the picture of pesticide use. This is one example of a relatively toxic material applied at a low rate that was replaced with a less toxic chemical applied at a much higher rate.

Chlorpyrifos

Chlorpyrifos had the sixth highest increase in pounds applied (Table 1). Its median rate of use in 1995 was 1.0 pounds per acre, a typical use rate, and this is also reflected in the fact that its use as measured by number of applications was one of the highest. The crops which had the greatest increase in chlorpyrifos use were cotton, orange, alfalfa, broccoli, and apple (Figure 8). By far, most of the increase in use from 1991 to 1995 was on cotton. Although cotton acreage increased (23 percent), chlorpyrifos use increased significantly more (2,200 percent).

Cotton: Chlorpyrifos is used on cotton mostly to control cotton aphids (Aphis gossypii). Until the last few years, cotton aphids were considered a minor pest of cotton. During the hot mid-summer, the cotton aphid usually remained in a small yellow form which had low reproduction and caused little problems. Since 1992, however, this aphid changed into a dark form in mid-season, reproduced prolifically, and caused serious problems to cotton. High aphid populations during June through August reduced the cotton yield and high populations later in the season after the bolls have opened created "sticky cotton" which causes problems in processing the cotton fibers. Many gins will not even accept very sticky cotton and if they do they will pay the growers a lower price.

The increase in chlorpyrifos use, which occurred most dramatically in 1994 and 1995, corresponds closely to the increase in aphid populations each year on cotton. Cotton aphids are also becoming resistant to a wide range of pesticides; growers may apply higher rates of pesticides to gain control of this pest.

Because of the increasing difficulties in controlling aphids and other pests in cotton and the desire of cotton growers to get other effective insecticides registered, DPR has been working with cotton growers in developing a resistance management plan for the major cotton pests. This plan has now been distributed to growers and if followed should prolong the effective life of many important pesticides and should keep pesticide use rates lower.


Conclusion and Discussion

Pounds of pesticide use increased in California from 1991 to 1995. However, it is important to examine which pesticides accounted for most of the increase, and the underlying causes of this increase. These factors are important for identifying emerging pest management challenges and focusing attention on strategies for their resolution. The use patterns of those active ingredients whose use had increased the most during this time period was examined. The six pesticides that had the largest increase in use accounted for an increase in 41 million pounds out of the 56 million pound increase of all agricultural pesticides used. Most of the use of these six pesticides were on just a few crops.

Claims in Rising of increasing use of probable carcinogens, category II organophosphates and carbamates, and restricted use materials are misleading because most of the increases are due to just two pesticides, metam-sodium and chlorpyrifos. Nevertheless, there are a number of pesticides classified as probable carcinogens whose use has increased between 1991 and 1995. Further research is necessary to understand the underlying factors behind increases in these materials.

Some may come away from an analysis of overall usage data with the impression that all pesticide use is increasing. Certainly, Rising erroneously suggested that "California fruits and vegetables are drenched with pesticides." Actually, the use of some pesticides, including some of the most toxic pesticides, is decreasing. Most of the increase in pesticide use is due to a few pesticides whose use is increasing because of pest management problems.

Improvements do need to be made in developing and promoting better reduced-risk pest management practices, but the picture is not as bleak as Rising makes it seem. Three of the six pesticides with the largest increase in use (sulfur, oil, or copper sulfate) are less toxic than most alternative pesticides and this is one of the reason these pesticides are used more. These reduced risk pesticides can play a key role in integrated pest management systems. DPR is playing a role in this process through its IPM Innovator Award program, through its Pest Management Grants program, and most recently through its Alliance program with key commodity organizations, growers, and researchers.

This report is only a start at looking at these issues. It did not present analyses of the rates of use (or "intensity" as discussed in Rising), regional differences in uses, or nonagricultural uses. More effort is needed to investigate these issues as well as follow up with more statistical analysis of the trends, look for correlations with weather data, as well as examine rates, number of applications, and acres treated for the particular pesticides and crops discussed here, as well as a few more of the major pesticides and crops, including the probable carcinogens. However, some of these factors are examined in the report that will accompany DPR’s release of 1996 pesticide use data.

DPR’s pesticide use database is an invaluable resource for understanding the patterns and trends of pesticide use in California. It is the largest and most complete such database any where in the world. Analysis of pesticide use patterns and trends can help inform the public, researchers, and growers where potential pest management challenges may lie and thus where more research and efforts to promote reduced risk practices could be directed. It could also be used to help determine which efforts to reduce risk are succeeding. But an analysis of trends must be informed by an understanding of the pest management decisions farmers are faced with, decisions that must be made in highly uncertain and complex ecological systems and that may even effect whether they can stay in business.



[1]Before full use reporting in 1990, only restricted use materials, such as 1,3-dichloropropene, were reported. The 1989 restricted use material report was published late.



Tables

This web site uses Adobe Acrobat PDF enhancements.

Table 1, PDF (8 kb) - Pounds of active ingredients (in 1000’s) used in California agriculture in each year from 1991 to 1995.

Figure 2, PDF (7 kb) - Changes in agricultural pesticide use from 1991 through 1995.

Figure 3, PDF (6 kb) - Pounds of sulfur (in millions) used on the crops which had the greatest increase in pounds used from 1991 to 1995.

Figure 4, PDF (6 kb) - Pounds of metam-sodium (in millions) used on the crops which had the greatest increase in pounds used from 1991 to 1995.

Figure 5, PDF (6 kb) - Pounds of oils (mineral oil, petroleum oil, etc.) ( in millions)) used on the crops which had the greatest increase in pounds used from 1991 to 1995.

Figure 6, PDF (6 kb) - Pounds of methyl bromide (in millions) used on the crops which had the greatest increase in pounds used from 1991 to 1995.

Figure 7, PDF (6 kb) - Pounds of copper sulfate (pentahydrate) (in millions) used on the crops which had the greatest increase in pounds used from 1991 to 1995.

Figure 8, PDF (6 kb) - Pounds of chlorpyrifos (in millions) used on the crops which had the greatest increase in pounds used from 1991 to 1995.


Appendix

Three tables are included in this appendix. Each table lists all pesticide active ingredients and the pounds of each pesticide used (Appendix Table 1), number of applications of each active ingredient (Appendix Table 2), and the cumulative number of acres treated by each active ingredient (Appendix Table 3) for each year from 1991 to 1995. These tables only include agricultural uses. Probable errors were removed before summing in Table 1. The top row of each table gives the total measure for all active ingredients in each year; the "Total" column gives the total measure for each active ingredient from 1991 through 1995; and the last column gives the change in use between 1995 and 1991. The totals in the top row of Table 2 are not exactly equal to the sum of all number applications of each active ingredient because some products contain more than one active ingredient. In calculating the total number of applications, each application of a product is counted only one time. The rows are sorted by change in use. All data are from DPR’s Pesticide Use Reports.

Table 1, PDF (65 kb) - Pounds of each active ingredient used in agriculture.

Table 2, PDF (66 kb) - Number of agricultural applications for each active ingredient.

Table 3, PDF (71 kb) - Total number of acres treated by each active ingredient in agriculture.