NEWSLETTER ARTICLES

Vegetables and Plant Pathology

Research has shown that the downy mildew (Bremia lactucae) pathogen of lettuce is in a continuing state of change. Some of the races of this fungus that were common ten years ago are now hard to find, and several new races now appear to be coming into prominence. Lettuce breeding to develop resistance to these new races of the pathogen continues as quickly as possible. However, it is evident that the breeding program must be augmented by an effective fungicide application program in order to continue production of high quality lettuce.

Maneb and fosetyl-Al are the current main fungicides used for the control of Bremia lactucae. However, with the review of all plant health chemicals that has been mandated by the new Food Quality Protection Act, the long- term availability of even these products is not certain. Therefore, the testing of new downy mildew control products needs to continue. Fortunately, several new low dosage fungicide products with interesting modes of action are being developed.

During the 1997 season, several downy mildew control trials were conducted in the Lompoc and Santa Maria Valleys. Several new fungicide compounds were compared with presently registered materials. The results of these trials are presented here.

SAMPLE COSTS FOR GROWING PROCESSING TOMATOES

UC Extension Ag. Exonomist Karen Klonsky, Pete Livingston, and I collaborated on a sample cost of production update for processing tomatoes in Yolo County. We received input from a number of different sources. A grower committee helped define common production practices. The report is an evaluation of costs for a hypothetical farm growing 900 acres of processing tomatoes as part of a 2,900 acre row-crop farming operation.

The format of the study is a departure from past studies. We are now using the UCD-developed database program "Budget Generator." Changes in input costs will be more easily calculated, so we may update more readily.

Compared to 1989 costs, the major changes were in (1) equipment prices as reflected in non-cash overhead; (2) land preparation; (3) planting costs, and (4) growing cost due to inputs, including fertilizers, labor, and fuel (Table 1). The one general area of reduced expense was cash cost to harvest, a measure of improved harvester efficiency. To reflect increased production, yields for the study were increased to 32 tons per acre, up from the 1989 study with 28 tons. Size of operation was also increased from 700 to 900 acres.

The Bottom Line: Total costs were $1,774 per acre. At an average yield of 32 tons per acre, growers are losing money at current prices. The break- even price would be $55.44 per ton. To only recover cash costs, $49 per ton are needed. While 32 tons per acre yields are respectable, costs are not recovered at current prices of less than $52 per ton.
Source: S.J.V. Veg. Crops Rpt. Fall 1997.

HOW SOON SHOULD WE REACT - ONE OPINION

During the last couple of months, there has been a major development in the emerging story of "environmental hormones." Last year, a study published in Science found an incredible in vitro synergistic effect between certain "environmental estrogens" at very low levels. (A synergistic effect is one in which the results of two separate exposures result in a far stronger effect than would occur if they simply caused an "additive effect.") The finding that such very low concentrations of these mixtures would produce an effect a thousand times stronger than expected was shocking. The abstract of the initial report stated:

"Combinations of two weak environmental estrogens, such as dieldrin, endosulfan, or toxaphene, were 1,000 times as potent in the HER (human estrogen receptor) -mediated transactivation as any chemical alone... This synergistic interaction of chemical mixtures with the estrogen receptor may have profound environmental implications." (Science 272:1489:1492, 7 June, 1996.)

In late July of this year, the authors formally withdrew the paper in a letter published in Science, stating that they had been unable to replicate the findings, and that other laboratories had been unable to do so as well. They also urged that this be taken into consideration because their results had been used widely. The withdrawal letter states:

"Also, since our publication in Science, others have been unable to reproduce the results we reported. Meanwhile, people in many walks of life have, on their own, put great weight on this report as the basis for much discussion, thought, and even public policy.

Whatever merit this publication contained, and despite the enthusiasm it generated, it is clear that any conclusions drawn from this paper must be suspended until such time, if ever, the data can be substantiated.

None (of the experiments we have conducted to explain the synergy) have provided a satisfactory mechanism to explain our earlier findings. Taken together, it seems evident that there must have been a fundamental flaw in the design of our original experiment." (Science 277:462-3, 25 July, 1997.)

They acted responsibly as scientists to retract their unrepeatable results.

The intent of my introduction and review of this situation is not to dismiss the issue (hormonal activity of environmental contaminants), which was unintentionally "punctuated" by this withdrawn paper. Certainly in the face of an imminent public health hazard, swift action must be taken. My intent is to ask the question should we react legislatively or through regulations to controversial findings? In addition, should "scientific results" be "codified" in laws and regulations which are difficult to change, and if so, how quickly? Scientific results will always be open to change because it is in the nature of science to change our knowledge and understanding. These are difficult public policy questions, because most of us feel that public policy should be based on sound scientific principles whenever possible. I don’t have answers to these questions, but they are the questions which must be addressed in the realm of public policy and public decision making.

Dr. Art Craigmill is Extension Toxicologist in the Department of Environmental Toxicology, U.C. Davis.

PROPER CALIBRATION PREVENTS PROBLEMS

Many problems seen in the field are due to poor calibration of delivery equipment. Failure to check and recheck application equipment can cost money. Here are some examples of the types of crop damage, yield loss, or chemical non-performance that are common.

Wrong Nozzles. It is easy to mix up nozzles on a spray system when setting up or reinstalling a spray boom. An 8008E mixed in with 8004E’s can make a substantial difference on two accounts. The larger 8008E will deliver more chemical, possibly injuring the crop. The amount of chemical mixed for the field could come up short, resulting in an underdose or the need to purchase more chemical to finish the job. A problem could also occur from mixing screen sizes, having clogged screens or failing to put a screen in the body. Check to make sure each spray tip has the same discharge rate.

Wrong Placement. When running injector shanks in a bed, they should be checked every few rounds to insure bolts have not loosened and slipped or the shank outlets have not plugged. While this may seem like a given, it is a lot better to find out a shank moved six inches out of alignment before you injected a 70-acre field than after you finished. The reason for a poorly growing tomato crop was once tracked back to a broken bolt on an injector shank, which allowed the shank to rotate back under pressure and squirt the preplant fertilizer in the upper inch of soil, where it was scrapped off with the bed shaper. Bent shanks can also be a problem.

Planter Problems. Seed spacing can be crucial with many crops such as carrots and onions which are not thinned usually, resulting in small-sized product and substantial yield loss. With other crops, improper spacing can also affect yield, perhaps not quite as significantly. Planting too much seed is also expensive. Planting too little seed can result in skips in the stand and oversize products. Seed depth is also important and should be checked frequently while planting. Changes in soil type can have an immediate impact on seed spacing and seed depth.

Installing Check Plots. Few growers make check plots in fields where the chemical (i.e., herbicide, fertilizer) was not applied. Without checks, it is often difficult to prove whether the suspected chemical caused the problem. With checks, there is evidence to verify the cause and to convince nonbelievers as to the facts. If agricultural chemicals are applied by ground by a commercial applicator, it is advisable to ask that check plots be left and marked in fields.

Records, Records, Records! The ancient Chinese had a saying that even the best memory is not as good as the faintest ink on a piece of paper. That still holds true today. Keep records to the row where you changed seed lots, include lot numbers and coding codes if any. Keep records of the kinds, amounts, and batch numbers of herbicide containers. Record times and dates of turning on sprinkler systems. In short, it is not possible to keep too many records, but it is easy to have too few.

Keith Mayberry is a Farm Advisor in Imperial County.