,, ~. DIAGNOSIS OF PHYTOTOXICITY FROM HERBICIDES IN SOILS. i r. Aencultural Extension University,of California. . I TA "''t'..l .

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1 il i r.. ' ~ "''t'..l,, ~.. DAGNOSS OF PHYTOTOXCTY FROM HERBCDES N SOLS Aencultural Extension University,of California. TA

2 \ -. The. authors are Arthur H. Lange, Extension Weed Control Specialist, Parlier; Clyde L. Elmore, Extension Weed Control Specialist, Davis; and Abdur-Rahman B. Saghir, Agronomist, American University, Beirut, Lebanon.. The University of California's Agricultural Extension programs are ovoiloble to all, without regard to race, color, or notional origin. Co o1 erau\"e F.xft n~i"" work n AJrri«ulturr nn l Honn F.r..,1mui, <'nllr<:'<' of A::rlt'ulturl', Uuivt>rsity of Cnli for11i, and Uuitud tilutch l.h vurtuwut u(.i,\att"icuhuro t o u1> rnttnj:. Hh lt"ihutud iu (u.rthurunt e uf th.a Achr. _uf Concreu of.ma;r 8, and.tuue ao, 1!114. Ocor1'1l JJ. Alcorn, Director, Cnlifornill A1'ricul&ural ExtouKiou Sonieo.

3 DAGNOSS OF PHYTOTOXCTY FROM HERBCDES N SOLS With the increased use of her~icides in California, information is needed about plant symptoms caused by chemicals applied to crops. Since very little is known about herbicide phytotoxiciiy (plant injury caused by herbicides), the effects of other pesticides, pollutants, environmental stresses, and nutritional problems are often misinterpreted as herbicide injury. For example, excessive use of animal wa stes or poor quality water (materials with a high salt content) often cause plant symptoms similar to those caused by herbicides. Nutritional chlorosis in trees and shrubs may be confused with simazine toxicity (figure 1). ' Persistent herbicides that were applied in excessiv'e amounts may occasionally produce phytotoxicity on subsequent crops that are sensitive to the herbicides. All modern herbicides are organic and, therefore, eventually break down in most field soils. Most herbicides break down in a few weeks. Others may remain in the soil for several months, and a few may last for more than a year. Most herbicides break down rapidly in warm, moist soils. De~tivation of herbicides is feasible. Soil-applied activated carbon has been used effectively to reduce crop injury. Soil enrichment with micro-organisms may also find its place in solving residue proble~s. Flooding may be a promising means of deactivating herbicides that break down under ~naerobic conditions o:p are readily leached. Figure 1. Symptoms of iron chlorosis (a) and. of injury caused by simazine at 8 to 16 lb. A. (b). Area between the veins lacks clilorophyll (green pigm.ent). ron deficiency causes a uniform whiteness of the leaf. with main veins the last to lose their color. With simazine, the leaf tissue nearest the veins stays green. Marginal leaf burn begins earlier in the simazine pattern development than in chlorosis caused by iron deficiency. A set of colored pictures comparing phytotoxicity symptoms of herbieides has been completed for publication but not yet financed. 1 ~1 'tt - l.;..' tt o U tt... t. :. d l

4 Field observations of crop injury caused by herbicides have stimulated more intensive studies on this problem. By add\ng specific amounts of herbicides to washed river. sand in the greenhouse, phytotoxicity symptoms and levels have been determined for several of the( more commonly used herbicides. Data in tables 2 and 3 show critical.herbicide levels that are phytotoxic to young. Lovell peach seedlings and several annual crops. Similar studies with simazine and other herbicides have also been conducted in field trials throughout California. These studies confirm the greenhouse iniormation on relative toxicities. However, the level of activity is usually higher in sandy soils than in clay soils. A list of tolerant and sensitive plant species, like the one in table 4, is useful in determining the source and level of herbicide residues in the soil. Chemical analysis is expensive and is not always related to the herbicides' biological activity. Soils have differing adsorptive qualities and greatly influence herbicide activity. An herbicide level of 1 ppm in sandy soils is more active than 1 ppm in clay soils. To find out if a soil has been treated with an herbicide at rates harmful to subsequent plant growth, it is usually possible to do a bioassay, using test plants. The herbicide present in the ~oil will stunt, twist, or kill the test plants, depending on the herbicide and its concentration. The bioassay technique probably bas even more valu~ in determining whether the phytotoxicity symptoms in a crop are the result of an herbicide O' some other cause,. t is easy to do a bioassay by planting test plants in small paper cups. Collect soil from the area you sus!lect has been treated and from an area you are sure is untreated. PROCEDURE 1. Take soil from depths of 0 to 2 inches, 2 to in suspected treated and in untreated areas. soil from each area. Greater depth may be extremely soluble. 4 inches, and 4 to 6 inches Collect two or three cups of advisable if the herbicide is 2. Plant seeds of sensitive and tolerant species in the treated and untreated soils. The plant that is sensitive to herbicides will show phytotoxicity symptoms or will be killed. The tolerant plant will be damaged less or will remain uninjured. Use more than one sensitive plant species to determine which herbicide is present. 2

5 3. Grow the plants under good cultural conditions for at least 20 days.. Be careful not to over- or under-water. Subirrigation is often best. 4. Evaluate tolerant and sensitive plant species, comparing the plant growth and foliar condition in s;spected treated soils with the plants grown in soil known to be untreatei.:l. Table 5 gives some examples of phytotoxicity symptoms caused by certain herbicides. t To limpiify informotion, trode names of products hove been used. No end.ouement of named products is intended, nor is criticism implied of similar products whi-ch ore not mentioned. TABLE 1. Common Names and Trade Names of Some of the Herbicides Listed in the Following Tables. Common Nome Trade Name Common Nome Trade Nome t " ametryne Evik diuron Kormex. omitrole Amitrol 90, Amizol EPTC Eptam otrazine AAtrex linuron Lorox benefin Bolan nitralin Planavin bensulide Betasan, Prefor nitrofen TOK bromacil Hyvar -X paraquat Paraquat butyl ate Su ton piclorom Tordon CDEC Vegodex prometryne Coparol chlarbromuron Moloran propazine Mi logorjlil chloroxuron Tenoran pyrozon Pyramin dolopon Dowpon - R7465 Devrinot DCPA. Dacthal simozine Princep. dicambo Ban vet terbocil Sin bar dichlobeni Cosoron terbutryn gr an diphenomid OymiJlil, Enide trhlurolin Treflon Registered trade name. 3.

6 ,,! i TABLE 2. Comparative Activity of Herbicides Applied to Lovell Peach Seedlings Growing in Nutrient-Fed Sand Culture. Herbicide, Average' Rate- Phytotoicicity Fresh weight (ppm) rating 2 (percent) o.os' imaz,ine o.s s.o o.os 0 88 diuron o.s o.os o.s 82 prametryne ilromacil 0.5 o~ ~ trifluralin DCPA 0.5' ' diphenamid TOO EPTC o.s 0 94 dalopon n amitrole paraquat ' ~ dicamba - ' ' l;o 96 piclor tmmnted check Average of four replicotion, per treatment. 1 Phytatoicicity roting, when 0 no effect; 3 distinct characteristic symptanu1; 5 chl01oai an4 marginal bvm or SO percent stunting; 10 all ti H# dead. 4

7 .,.!~. ~ " l TABLE 3. A Comparison of Herbicide Activity on Germinating Crcips.' Average Phytotoxicity 2 Rote Sugar Herblci.de (ppm) Com ~arley Wheat Cotton beet Tomato Melon Lettuce 0.1 O 0, ti o-zifte s dturon ' ' o p,_etrylle O. l linuron thomocil terbocil clichlobenil propozine l bensulide diphenamid l DCPA triflurolin MSMA check 'Herbici-des applied in water suspension to washed, nutrient-fed river sand11.application made after seeding d before germination. 2 Aveu19 of four t plication11, Phytatoidcity rating: 0 no effect; 5 -half 11tand or half-11ize planh; 10.. oil plorts foiled to 9erminate or germinated and died. 5

8 .. TABLE 4. ndicator Plont Spec:ies for Herbicides and Groups of Herbic'ides. Herbicide Tolerant P lants Susceptible Ptonts.. cotton pyrozon Milo, sugar beet Tom.ato, cabbage, bean, brocc:oli, Triozines..:...simazine, Corn, milo Sutor beet, tomato, lettuee, atrozine (small grains-intermediate) Ureos-diuron, linuron,. Groundsel (~ vulgaris), Sugar beet, tomato chlorbromu r_!:!n some orn amentals Uroei ls-terboci, bromoc:il Citrus and mint All crops e~.cept citrus and mint Cari;"omates-EPTC, butylote, Bean, alfalfa Milo, borley COEC Dinitro onilines-triflurolin, Tomato, safflower, sunflower, Sugar beet, milo, millet, nitrolin, benefin cotton, carrot bornyordgross ( Echinoc:hloa) 1 (barjey-intermedi ate) dicomba and piclorom Mi lo, ryegross, smc:tll groins Bean, safflower., alfolfo diphenomid and R7465 Tomato, bean, pepper Barley, mile> dichlobeni. Milo, c;om,(smoll groins- All field and vegetable crops-... ~,,: intermediate) corrota nitrofen Broccoli, cabbage Tomato, (lettuce-intermediate) M.SJ ~A Broccoli, bean Peanu.t, rice, milo dot llpon 8f'oodleof crops Grasses DC PA Barley, onion Sugar beet, mi lo, lettuce, (tomatointermediate). TAE LES. Examples of Herbicide PhytotoxiC:ity Symptoms in Sensitive Grassy and Broadleaf Plari ts. Symptoms Herbicide Present G1 la$s8$ Stunting c:tnd root stubbing Twisting Chlorosis (Symptom may appear after about lo to 12 days.) triflurolin, benefin, diphenomid, nitrolin, or DCPA EPTC or dolapon diphenomid, simozine, or atrozine 81 'Padleaved Plants StuntiAg and/or loss of stand Twisting and stunting Chlorosis (veinal) Chlorosi s (interveinol) diph!tnamid, trifluralin, or nitralin 2,4 0 al! dicombo diuton, chl010.xuron, bromoci t, terboci, prometryne,. Cll'Aetryne, or terbutryn simozlne, otrozine, or linuron ' &