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In This IssueWhy Your Insecticide May Not Be Working as Well asYou Would Like10 Useful Rules for Fungicide ApplicationsSpray Pressure and Nozzle TypeUpcoming EventsTemperature and Precipitation July 21 and July 27Temperature and Precipitation July 14 and July 20

Why Your Insecticide May Not BeWorking as Well as You Would Like(Rick Foster, fosterre@purdue.edu, (765) 494-9572) & (Laura Ingwell,lingwell@purdue.edu)

It’s not uncommon for us to get calls from growers who areexpressing concern about a particular insecticide productthat is not working as well as the growers would like. Often,growers will suggest that Product X is no good or that thetarget insect has now developed resistance to that particularinsecticide. Before we jump to conclusions, we need toconsider a number of possible causes for poor performanceby an insecticide. Here are some questions to consider if youare not getting the control you would like.

Are you using the right product? Every fall, a1.group of vegetable entomologists from throughoutthe Midwest thoroughly revise the insecticiderecommendations in the Midwest VegetableProduction Guide (ID56). The products we list in theguide are the ones that we believe work for aparticular pest, based either on research trials orthrough our experience with growers. That’s why wealways like to hear from growers when a new productcomes along to determine if they are satisfied withthe control they received. Sometimes a product willlook good in small trials but not so good in large fieldsituations, so that is good information for us to know.Related to this question is “have you identified thepest correctly?” Products can vary greatly on how wellthey control various pests, so correct identification is

critical. Most of you deal with the same insect yearafter year, so this would not be an issue. However, forsome newer or less frequent pests, make sure you aretreating for the right pest.Was your timing right? For many insect pests (for2.example, corn earworm in sweet corn), timing iscritical. Missing the optimal timing for earworms by acouple of days because of a muddy field, can greatlyincrease the amount of damage when pressure ishigh. Timing is not as critical for some other insectsbut growers should be sure to use the economicthresholds that we suggest. We purposely set thoseconservatively because we know that cleaning up anextremely high population of some pests can beextremely difficult.How is your water? Many insecticides are subject to3.degradation by alkaline hydrolysis. Each insecticidehas an optimal range for the pH of the water in whichit is mixed. Generally speaking, water should be eitherneutral or slightly acid (pH of 7 or below) to avoidbreakdown of the active ingredient. If your water, likemuch of the water in Indiana, has a pH higher thanthe optimal range for your insecticide, you shouldtreat the water to lower the pH and improve yourcontrol. Likewise, some insecticides are rendered lesseffective by excessively hard water, another commontrait of water in Indiana. Again, for some insecticides,lowering the level of hardness will improve control.How is your coverage? An old expression on how to4.get good insect control with insecticides is “the rightinsecticide at the right place at the right time.” Forinsecticides that are not systemic (don’t movethrough the plant), good coverage is essential. We’vebeen doing some research on the control we receivefrom different sprayers or boom types for earworms insweet corn. We used water sensitive cards tomeasure the amount of coverage we are getting onthe ears and compared that to the level of infestationof earworms in the ears. What we found is that thereis a very high correlation between the amount of

Issue: 648August 2, 2018

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coverage and the control we received. I encourage allgrowers to purchase some water sensitive cards andtest their sprayers to see what level of coverage theyare receiving. If you do that and are not getting thecoverage you would like (and your control is notsatisfactory), here are some options for improvingyour coverage: increase your gallonage, increase yourpressure, use drop nozzles for sweet corn, increasethe number of nozzle tips, change the type of nozzletips, drive slower.Is your sprayer properly calibrated? When was5.the last time you calibrated your sprayer? It should bedone at least annually. Nobody likes going throughthe process of catching water from each of the nozzletips and doing the math to see if your rates arecorrect, but it is a necessary evil if you want to getgood control. Likewise, if you are spraying a 40 acrefield, you are not really spraying 40 acres. You haveto account for fence rows and field margins whencalculating how much area you are spraying.Is your sprayer in good working order? If you6.calibrate your sprayer, you will quickly find out ifsome nozzle tips are clogged or worn. There shouldbe less than 5-10 percent variation between theoutput of different nozzles. If the variation is greaterthan that, the nozzles should be either cleaned orreplaced. Have you checked all your hoses to makesure that there are no leaks? Insecticide leaking froma hose is not going to kill any insects and that meansyou are putting on a lower rate than you intended onthe plants.What time of day are you spraying? Most7.insecticides are broken down by heat and sunlight sothe optimal time to spray insecticides is late eveningor at night when temperatures are dropping andsunlight is fading. Many insect pests are nocturnal, sospraying right before they become active will increasethe control of that first night. Also, when spraying inthe heat of the day, some of the insecticide willvolatilize before it reaches the plant, again resultingin a lower rate of residue on the plant. An addedbenefit of spraying in the evening/night is thatpollinators will have left the field and any harm doneto them will be minimized.What are you mixing with your insecticide?8.Some insecticide/fungicide combinations are notcompatible. Be sure to check the labels before mixing.Also, check the label to see if the manufacturerrecommends any adjuvants be mixed with theinsecticide.What is the weather like? Weather can be an9.

important factor in the effectiveness of an insecticideapplication. For example, the pyrethroid insecticides(Warrior®, Capture®, Baythroid®, Mustang Maxx®, etc.)tend to break down more quickly when temperaturesare high, upper 80s or 90s. If you are experiencingdecreased control with pyrethroids during warmperiod, consider switching to a non-pyrethroid option.In contrast, products that need to consumed by thepest, such as Bt products, tend to be more effectivewhen temperatures are warmer because the insectsare more active and consuming more insecticide asthey feed. Rainfall can also be a big factor.Insecticides vary greatly in how well they adhere tothe plant after a rainfall. As a general rule of thumb, ifthe insecticide completely dries on the plant beforerain occurs, a light rain will have little effect on theresidues. The heavier the rain event, of course, themore insecticide will be washed off the plant. Ideally,you would want to spray after the rain, but that oftenis not possible because the fields are too muddy foryour sprayer to pass through the field.Is the target pest resistant to the insecticide?10.We purposely listed this possibility last because, whileresistance is a real and increasing problem, it isusually not the reason for poor control. In recentyears, corn earworms developed resistance topyrethroid insecticides that had provided excellentcontrol for many years. We were able to confirm thatwith laboratory studies, but growers should not jumpto conclusions about resistance based on a singlecase of poor control.

10 Useful Rules for FungicideApplications(Dan Egel, egel@purdue.edu, (812) 886-0198)

Since there is an article about the application of insecticidesin this issue, below I list 10 rules that will help vegetablegrowers apply fungicides effectively and safely.

Apply fungicides prior to the development of disease.1.Although many fungicides have systemic (“kickback”) action they will not completely eradicatediseases after they have started. And by the time asingle disease lesion is observed in the field, manymore lesions too small to observe are already workingat your crop. Most systemic fungicides move less thanan inch toward the tip of the plant or may just movefrom the upper to the lower side of the leaf.Use shorter spray intervals during weather conducive2.to plant disease. Each plant disease has its own

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“personality” and thus prefers different weather.However, most plant diseases require leaf wetness.Therefore, during periods of rain and heavy dews,more frequent fungicide applications are a good idea.The normal range of spray applications is every 7 to14 days. Cantaloupe and watermelon growers havethe guesswork taken out of this process with a PurdueUniversity program known as MELCAST. Ask theauthor for more details by calling (812) 886-0198 orgo to melcast.info.Apply fungicides before a rain if possible. Water is3.necessary for most fungal spores to infect a plant andfor the splash dispersal of many spores. Therefore,apply fungicides before a rain if it appears that thefungicide will have a chance to dry before the rain. Itis not necessary to apply fungicides again after everyrain. Most fungicides have a good sticker and willpersist through rains pretty well. The MELCASTprogram takes into account the affect weather has onfungicides.Know when to alternate fungicides. Systemic4.fungicides, those with a single mode of action, ifapplied again and again in sequence, may causedisease causing fungi to mutate into a form resistantto the fungicide. It is always a good idea to alternatefungicide applications from one FRAC code (MOAcode) number to another. Read the label carefully tofind language about fungicide alternation. Contactfungicides with a FRAC code of M like chlorothaloniland mancozeb are very unlikely to cause suchmutations and therefore may be applied in sequence.Although some fungicides may have designationssuch as M01 or M02, any fungicides with an M doesnot need to be alternated. (Products with copper asan active ingredient may have resistance issues-seearticle about bacterial spot of tomato in the last issueof the Hotline.) Table 32 in the Midwest VegetableProduction Guide http://mwveguide.org/ will helpgrowers alternate fungicides.Timing of fungicide applications is more important5.than nozzle type and spray pressure. Studies here insouthern Indiana as well as by researchers in otherareas of the country have found that nozzle type andspray pressure doesn’t make as much difference aswe once thought. See the article in this issue of theHotline. In general, the more water one uses per acre,up to about 50 gallons, results in better coverage.Some diseases cannot be managed by foliar sprays.6.Problems caused by soil borne fungi or nematodescannot be controlled with foliar fungicides. Examplesof these types of problems would be Fusarium wilt of

watermelon or root-knot nematodes of tomatoes.Also, be certain that the problem you observe is reallya disease. No amount of fungicide will improve aproblem caused by soil fertility. Send a sample to thePurdue Plant and Pest Diagnostic Laboratory to findout the official diagnosishttp://www.ppdl.purdue.edu/ppdl/index.html.Use copper products for bacterial diseases. For the7.most part, copper products are more effective againstbacterial diseases than they are against fungaldiseases.Some diseases require specialized fungicides.8.Diseases, such as downy mildew and Phytophthorablight, may require specialized fungicides. It may bewasteful to apply specialized fungicides all seasonlong for diseases that are not a threat. For example,downy mildew of cucurbits usually does not arrive inIndiana until late in the season.Double-check the label for details. Rates may vary9.widely based on label changes and differentformulations. While you are checking the rate, alsomake sure that the crop and disease are on the label.(Can this fungicide be applied in the greenhouse?) Didyou get the rate from the Midwest VegetableProduction Guide for Commercial Growers?http://mwveguide.org/ Check the label anyway.Play it safe. Always adhere to the Post-Harvest10.Intervals, Re-Entry Intervals and Worker ProtectionStandards listed in the label. No one wants anaccident or lawsuit. Besides, the label is the law.

Spray Pressure and Nozzle Type(Dan Egel, egel@purdue.edu, (812) 886-0198)

Many years ago, I was told that to successfully usefungicides on vegetables, one must use high spray pressuresand hollow cone nozzles. However, I had trouble finding anyresearch on this topic, just rumors. So, I did my ownresearch.Dennis Nowaskie, Superintendent at the Southwest PurdueAgricultural Center (SWPAC) built a single row sprayer thatcould be used to vary nozzle types between flat fans andhollow cones and spray pressures from 30 to 150 PSI. Weused the sprayer to conduct experiments on Alternaria leafblight of cantaloupe during three years of field tests. Thefungicide we used to try to manage this disease was thecontact product chlorothalonil (trade names include Agronil®,Bravo®, Echo® and Terranil®). Phillip Harmon, now aprofessor at the University of Florida, was my co-author onthis paper.

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Try as we might, we could not find any statistical differencesin disease severity or yield between any of the nozzle typeor spray pressure treatments. We also used water sensitivepaper to measure coverage at each treatment; we found nostatistical differences in the coverage of water sensitivepaper as a result of spray pressure or nozzle type.Regardless, of the nozzle type or spray pressure there wasno statistical difference in coverage. This research was oncantaloupe and Alternaria leaf blight. However, I have reasonto believe that the research applies to other situations aswell. Read on for research on other crops and diseases.University of Florida researchers lead by Tom Kucharekfound that regardless of whether flat fan or hollow conenozzles were used, no difference in disease severity wasobserved in the following diseases: early or late leaf spot ofpeanut, bacterial spot of pepper and blast or purple blotch ofonions. Kucharek also found that spray pressures rangingfrom 50 to 250 psi made no differences in disease control inearly or late leaf spot of peanut.In general, higher spray pressures (and to some extent,hollow cone nozzles) are often linked with smaller dropletsize. Small droplet sizes are often associated with bettercoverage. If this is so, why wasn’t I able to find betterdisease control or coverage using hollow cones and highspray pressures? One reason may have to do with where thespray ends up. If one watches a boom sprayer from adistance, it is often possible to see a mist that is generatedby the spray that floats across the field. Clearly, this mistrepresents water plus active ingredients that may very wellnot end up in contact with the crop. It may be that whilesmall droplet size helps to increase coverage, too high apopulation of small droplets increase the amount of non-target impacts.I was not able to obtain funding for the question of howmuch water per acre to use for fungicide applications. Myobservations are that one should use between 20 and 50gallons per acre. My personal opinion is the more the better,within this approximate range.Based on this research and the work of others, it might bethat we have overestimated the importance of highpressures and small droplets in protecting vegetables fromdiseases. It seemed reasonable that more drops wouldprovide better coverage and less disease. However, the datadoesn’t indicate this at all. If buying a house is location,location, and location, then using fungicides on cantaloupe,and perhaps other vegetables, is all about timing.The timing of fungicide applications is usually moreimportant than nozzles and pressures. Some of my thoughtson fungicide timing are given in this issue of the Hotline onfungicide application hints.

Upcoming Events

Daviess Co. Produce Production MeetingDate: Aug. 14, 2018 6:30 pm – 8:30 pmLocation: Daviess Co. Produce Auction, LLC, 5567 N 900 E,Montgomery, IN 47558

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Small Farm Education Field DayDate: Aug. 30, 2018Location: Purdue Daniel Turf Center (1340 Cherry Lane,West Lafayette, IN 47907) and Purdue Student Farm (1491Cherry Lane, West Lafayette, IN 47906)

Greenhouse and Indoor HydroponicsWorkshopDate: Sept. 5, 2018Location: 625 Agriculture Mall Drive, West Lafayette, IN47907

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Temperature and Precipitation July21 and July 27(Wenjing Guan, guan40@purdue.edu, (812) 886-0198)

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Temperature and Precipitation July14 and July 20(Wenjing Guan, guan40@purdue.edu, (812) 886-0198)

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Vegetable Crops Hotline © Purdue University - vegcropshotline.orgEditor: Wenjing Guan | Department of Horticulture and Landscape Architecture, 625 Agriculture Mall Dr., West Lafayette,

IN 47907 | (812) 886-0198