SIGNS, SYMPTOMS, INJURIES - CAUSED BY HERBICIDES ? Bill B. Fischer*

Today, herbicides are essential tools used on nearly every acre of major fruit, vegetable, grain, forage and fiber crop produced in California. And, if the regulatory agencies were more understanding, manufacturers of herbicides more benevolent and attorneys less rapacious, every acre of minor crops would be treated with herbicides as well, legally. Herbicides are used because they can significantly reduce the drudgery and cost associated with preventing, destroying or controlling the growth of unwanted competing vegetation - weeds. Everyone who ever attempted to grow a certain plant in preference to another realized that unplanted and unwanted plants (weeds) growing in the same area had to be destroyed because they deprived the desirable plants (crops) of moisture and nutrients. Weeds interfere with many essential cultural operations. They can increase the cost of harvest,. whether it is done by hand or machines. Weeds can significantly reduce yield as well as the quality of the crop. They can adversely affect the aesthetic value of our environment and the usefulness of our recreational areas. Without the effective and intelligent use of herbicides, farmers in the United States could not grow enough food and fiber to feed and clothe themselves and 70 to 80 other human beings in this country and in other areas of the world.

Good Old Days? Before herbicides were invented, in "The good old days" to some, if the planted seed failed to emerge, or when plants turned yellow or died, it was attributed to the wrath of gods. Farmers consulted their shamans who performed dances and chants pleading to their gods for the correction of the problem and for an abundant harvest. Today, herbicides are widely used, especially in California. If seeds fail to emerge, or plants are retarded in growth, turn chlorotic or necrotic, no dances are performed but the label is read and reread and everyone maneuvers as to where to lay the blame. Instead of pleading to the gods, attorneys supplicate in courthouses for dollars. Neither method is very helpful in solving the problem or preventing its recurrence. Signs, Symptoms and Injuries

It is well known that plants require about sixteen chemical elements to grow and produce their fruit and fiber. Some of these elements are required in large quantities, others in minute amounts. It is also well known that an inadequate supply, or excessive amounts of these essential elements can cause certain signs, symptoms and injuries. We observe these as yellowing, purpling, stunted growth or death of the plants. *Farm Advisor,-UniversTty of-California Cooperative Extension,-Fresno County--

169 There are a large number of insects, bacteria, fungi, viruses and nematodes that can also cause symptoms and injure plants. Cultural practices such as poor land preparation, inadequate or excessive amounts of water can adversely affect the growth of plants as well. These problems can be diagnosed through observable signs and symptoms. At times, chemical analyses of the soil and plants are required to accurately identify the causative agent or deficiency. In the latter half of the twentieth century, a revolution occurred in our knowledge and ability to combine chemical elements to protect our crops from harmful organisms and from competing unwanted vegetation. These chemical compounds are called insecticides, fungicides, nematocides, herbicides and so on. Collectively they are referred to as pesticides, or crop protection chemicals. In this paper I will limit my discussion to herbicides. Herbicides - Plant Killers or Crop Savers? We need to keep in mind that all herbicides are plant killers, that is the only reason for using them. However, herbicides are also crop savers, that is why we use them and will continue using them in the future. Effective use of herbicides saved many farmer's pepper crops because they were able to selectively kill the unwanted plants in the field. Without the use of herbicides, tomatoes could not be grown profitably or harvested efficiently. Weeds adversely affect not only the yield of cotton, but the quality of the fiber. There are many such examples one can cite. Cultivators cannot be used in crops such as onions and carrots where multiple rows are planted on a bed. Hand weeding is effective, but only the use of selective herbicides offers viable economic alternatives. In spite of the increasing costs involved in developing and marketing herbicides, often imposed by questionable rules and regulations, they will continue to be developed and used because we will not be able to grow many crops profitably without them. The Safe and Effective Use of Herbicides Some people erroneously assume that the availability and use of selective herbicides greatly simplifies farming. That is not so; farming was less complicated, required less brain but more brawn when the unwanted vegetation was pulled by hand or controlled with repeated hoeings and cultivations. To use herbicides safely and effectively we must be cognizant of the numerous factors that can influence their effect on the crop plants and the weeds. Factors such as soil type, temperature, physiology of the crop and weeds, moisture, method of application, timing of application, rate of application and accuracy of application. These are but a few, and certainly not all the variable factors that can influence the selectivity and safe use of herbicides. It should not surprise anyone that under certain conditions, farmers will experience poor performance and, at times, they will observe signs, symptoms and injuries caused by herbicides. However, the potential benefits are economically so advantageous that farmers should be willing to assume a certain amount of risk in using them.

170 During my thirty-three years of experience in evaluating the performance of herbicides and working with farmers and pest control advisers, I found that poor performance, symptoms and injuries caused by herbicides are primarily due to: improper timing of their application, miscalibration of the sprayer, poor land and seedbed preparation, gross neglect of the instructions printed on the label, improper identification of the weed infestation and poor selection of herbicides. There is a tendency to attribute all problems, all signs, symptoms and injuries, to herbicides if they were used in the field, regardless of the cause. Often, erroneous diagnosis is made weeks and months after the herbicide was applied. In many situations, the problem was not properly diagnosed in the field or laboratory but argued by lawyers in a court, and the verdict was rendered by people who knew nothing about growing the crop let alone the proper use of herbicides. Diagnosing Signs, Symptoms and Injuries It is relatively easy to determine whether signs, symptoms or injuries are caused by herbicides if the diagnosis is made early and all factual information is available, relating not only to the use of herbicides but to all other cultural practices performed. We must be careful and methodical in our analysis of the problem and avoid making hasty decisions. To accurately diagnose problems and to avoid embarrassing and costly errors, we need to familiarize ourselves with signs, symptoms and injuries that may be caused by herbicides. When we observe stunted growth, chlorosis or necrosis, what we see are signs of abnormality • Until we know the cause, it is but a warning sign alerting us for further investigation. Only after it is accurately determined that the yellowing of the leaf blade on the tomato is caused by Sencor (metribuzin) can we call it a symptom, because yellowing can also be caused by nitrogen deficiency, zinc deficiency and virus diseases. Until we know the causative agent we cannot call it a symptom. Another example, 2,4-D, 4-CPA, Roundup (glyphosate) and Banvel (dicamba) can cause deformity of the meristems and abortion of the flowers on tomato plants, but only after it is correctly determined which one was applied or drifted into the field can we call it a symptom caused by Roundup, 2,4-D, 4-CPA or Banvel. A sign or symptom does not necessarily result in inJury. Treflan (trifluralin) applied postemergence in a cantaloupe field may result in symptoms of shortened internodes, deformity or veinal constrictions of leaves, not unlike mild 2,4-D symptoms. These symptoms are short lived and do not result in delayed maturity, reduced yield or quality. Injury implies economic loss due to reduction or loss of the stand, delay in maturity and reduction in marketable yield. Symptoms caused by Kerb ( pronamide) on seedling lettuce can be tolerated because it does not result in delayed growth or injury, but Gramoxone (paraquat) drift on spinach is intolerable because it makes it unmarketable. Drift of defoliants on lettuce can decrease the value of the crop and/or increase the cost of its production because the wrapper leaves have to be removed prior to packing.

171 Not Everyone Should Use Herbicides I do not know of any herbicide on the market that, under certain circumstances, will not cause symptoms such as temporary growth retardation, epinasty, chlorosis or necrosis. Unwillingness to tolerate any growth retardation or other temporary symptoms, precludes the use of certain herbicides. Goal (oxyfluorfen) is a very effective, extensively used herbicide for weed control in onions but it can cause slight curling, necrotic spotting and temporary growth retardation. Under favorable growing conditions, these symptoms are short lived and have less adverse effect on the growth and yield of the onions than the presence of weeds. Certain herbicides do not produce readily identifiable foliar symptoms. Among these are the dinitroanilines such as Treflan (trifluralin), Prowl (pendimethalin), Balan (benefin), etc.. They can adversely affect the development of secondary roots resulting in retarded growth, therefore, their shallow incorporation as preplant herbicides is essential. There are many other herbicides that cause root growth retardation. A few examples are Furloe (CIPC), Devrinol (napropamide), Lasso (alachlor), Dual (metolachlor), Eptam (EPTC), Tillam (pebulate) and others. But, compacted soils and soils high in salinity can adversely affect normal root development and shoot growth. Numerous herbicides interfere with photosynthesis through inhibition of electron transport, ATP synthesis, carbon metabolism and nitrogen assimilation resulting in chlorosis (yellowing). The pattern of readily observable chlorosis produced by herbicides differ, but they can be used only as a clue or diagnostic tool in determining what caused the symptom. When we had relatively few herbicides, we were able to differentiate symptoms caused by urea herbicides like Karmex (diuron) and Princep (simazine), a triazine. When we observed veinal chlorosis and the interveinal areas remained green, we were fairly sure it was caused by a urea herbicide. When the veins of the leaf remained green and interveinal areas were yellow we were confident it was caused by triazines. These good old days are over. Today we have a number of herbicides, including triazines like Igran (terbutryn) that cause veinal chlorosis, and many herbicides, including ureas, that cause interveinal chlorosis. Roundup can cause symptoms not unlike those caused by 2, 4-D. Symptoms caused by Solicam ( norflurazon) are not unlike those caused by Sinbar (terbacil). Several herbicides (Sonar, Racer, FMC-57020, SC-0735) cause symptoms not unlike Amitrole (amino triazole), etc. There are nutritional deficiencies and virus diseases that can cause symptoms similar to those caused by herbicides. Curly-top, a virus disease on peppers, is not unlike symptoms caused by an excessive rate of Enide (diphenamid). Residual properties of certain herbicides can compound the problem and complicate the diagnosis. One needs to be familiar with symptoms caused by herbicides. This knowledge can facilitate diagnosis, narrow leads and minimize costly chemical and laboratory analyses. The temptation of giving a swift diagnosis should be avoided and symptoms should not be attributed to an herbicide unless one is certain that herbicide was used in the field. The wrong diagnosis can be not only embarrassing, but very costly.

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Caparol (promotryne) was applied in cotton as a directed spray for the control of black nightshade. A couple of weeks later, all the leaves on the cotton plants had signs of chlorotic blotches. I was called out to confirm the diagnosis made by the PCA and the representative of Ciba Geigy that it was caused by Caparol. I suggested that the symptoms were more like those caused by a broadcast application, and not those caused by a directed spray application of Caparol. I suggested that the signs resemble those caused by Bladex (cyanazine). To make a long story short, chemical analysis confirmed the presence of Bladex, and it was later learned that the sprayrig used to apply a miticide on the cotton had been used for the application of Bladex on corn. Importance of Early Diagnosis The importance of early diagnosis cannot be over emphasized. Dried up leaves or dead plants are very poor diagnostic tools. Diagnosing problems caused by herbicides is quite simple when accurate information relating not only to the rates of herbicides used and methods of their application is known but all other cultural practices are examined. Unfortunately, in many instances, this is not made available or is conveniently forgotten, and to ascertain the true cause of the symptom or injury, one must assume the role of a Sherlock Holmes. In many tomato and sugar beet fields where replant or starter fertilizers are placed too shallow and the primary roots were injured, the erroneous diagnosis of herbicide damage is made. To illustrate the importance of candor, I was called to confirm a diagnosis that someone made in two lettuce fields planted following a crop of cantaloupe in which Sonalan (ethalfluralin) was used. In large, irregularly shaped areas in the field, the lettuce failed to emerge or died soon after emergence. On some of the emerged plants the hypocotyl was girdled or only one side appeared desiccated. On these plants the secondary roots appeared normal. I did not agree with the early diagnosis. I visited the field several times and each time I learned that something else was applied in the field such as manure, sulfuric acid and commercial fertilizers. I learned that the field was infested with field bindweed and the infested areas were sprayed with Roundup prior to planting of the lettuce. Soil analyses for nutrients, salt, pH, Sonalan, Treflan and Kerb were made, but the results did not adequately explain the signs we observed. Plant samples were submitted to pathologists, and entomologists were also consulted. After my third or fourth visit, I heard that Goal (oxyfluorfen) may have been added to the Roundup to obtain better control of the field bindweed. Subsequent soil analyses confirmed the presence of oxyfluorfen in all areas where the lettuce did not emerge or the plants expressed signs of herbicidal activity. If all facts would have been available when the problem was first observed, the proper diagnosis could have been made. The high costs of chemical analyses could have been avoided, and possibly, following some soil manipulation, the field could have been replanted. We are fallible human beings and we all make mistakes. Some people make more of them than others. Some people will misuse herbicides no matter what you tell them just like they misuse other tools, equipment and cars. If they did not, we would need fewer insurance companies and much fewer attorneys.

173 Symptoms caused by herbicides will be with us as long as we continue using herbicides. And, we will keep on using them more extensively because the alternatives are much more expensive, less readily available, often hard to manage and provide shorter lived control. Herbicides are crop savers, but only when they are used safely, effectively and economically. Signs, symptoms and injuries will be encountered in the production of our crops, and they will be attributed to herbicides rightly or wrongly. Our ability to diagnose the problems will be taxed, but we cannot escape the responsibility.

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