COOPERATIVE EXTENSION SERVICE • UNIVERSITY OF KENTUCKY COLLEGE OF AGRICULTURE, LEXINGTON, KY, 40546 ID-91 An IPM Scouting Guide for Common Problems of Cucurbit Crops in Kentucky Agriculture and Natural Resources • Family and Consumer Sciences • 4-H Youth Development • Community and Leadership Development EXTENSION An IPM Scouting Guide for Common Problems of Cucurbit Crops in Kentucky This manual is the result of efforts of the University of Kentucky Vegetable IPM team. Funding for this publication is from the University of Kentucky Pest Management Program. UK Vegetable IPM Team Kenny Seebold, Extension Plant Pathologist Timothy Coolong, Terry Jones, and John Strang, Extension Horticulturists Ric Bessin, Extension Entomologist Cheryl Kaiser, Editor Cover: Powdery mildew (on the foliage) and potyvirus complex symptoms (on the fruit) on pumpkin. Kenny Seebold Contents Photo Credits ong before the term “sustainable” became a Lhousehold word, farmers were implement- 4 .. Physiological and Nutritional Disorders Many of the images in this manual came from ing sustainable practices in the form of integrat- the personal collections of members of the UK ed pest management (IPM) strategies. IPM uses 8 .. Insect Pests Vegetable IPM Team. However, in some instanc- a combination of biological, cultural, physical, 12 .. Diseases es images were provided by outside sourc- and chemical methods to reduce and/or manage es. Credits for those images are listed below by pest populations. These strategies are used to 21 .. Chemical Injuries owner, affiliation, and image number. minimize environmental risks, costs, and health hazards. Pests are managed to reduce their neg- Clemson University ative impact on the crop, although pests are USDA Cooperative Extension Slide Series rarely eliminated. Bugwood.org—1, 39 Essential to the IPM approach is scouting and Colorado State University monitoring of diseases, insects, weeds, and abi- Acknowledgements Howard Schwartz, Bugwood.org—32b otic disorders in order to identify potential prob- The authors gratefully acknowledge the Oregon State University lems before they result in serious losses. The key following reviewers: Cynthia Ocamb—28 to effective monitoring is accurate identification. This guide covers the more common abiotic and John Hartman, Paul Vincelli, Paul Bachi, University of Georgia biotic problems that occur on cucurbits (Cucur- Julie Beale—University of Kentucky David Langston, Bugwood.org—4, 6, 10, 32a, bitaceae family) in Kentucky. This plant group, David Langston—University of Georgia 40a, 46, 48 also referred to as vining crops, includes cucum- ber, muskmelon (cantaloupe), watermelon, spe- University of Kentucky cialty melons, squash, pumpkin, and gourds. Julie Beale—31a John Hartman—26a, 41a, 43c This guide has been designed to serve as a com- William Nesmith—35a, 40b, 41b panion to the University of Kentucky publication Vegetable Production Guide for Commercial Grow- University of Maryland ers (ID-36), available from your county office of Gerald Brust—30 the Cooperative Extension Service or online at Virginia Tech http://www.ca.uky.edu/agc/pubs/id/id36/id36. Mary Ann Hansen, Bugwood.org—37 htm. Within ID-36, you will find detailed informa- tion on the production of cucurbits, fertility, and Sponsored by Kentucky IPM pest management. Should you need addition- al information on the problems covered by this Trade names are used to simplify information in this publication. No endorsement is intended, nor publication or for a problem not discussed here, is criticism implied of similar products that are not named. This guide is for reference only; the most recent product label is the final authority concerning application rates, precautions, harvest intervals, please consult ID-36 or contact your county agent. and other relevant information. Contact your county agent if you need assistance. Physiological and Nutrient Disorders 1 2a 2b Blossom end rot on watermelon fruit. Drought (a) and drought/sunburn (b) symptoms on pumpkin. 1. Blossom end rot is a physiological disor- kins fail to gain appropriate size, which affects 3 der observed in many cucurbits as well as other yields. A loss of foliage during drought will also crops (for example, tomato and pepper). It typi- result in sunburn of the fruit. cally appears as a general rot at the blossom end Management—Irrigate when necessary. of developing fruit. Blossom end rot is usual- ly the result of inadequate or uneven irrigation, 3. Flood damage symptoms often appear as high humidity, or other factors that slow the nutrient deficiencies or a generalized yellowing. movement of water through the plant. Since cal- Prolonged exposure to flooded soils will result cium is taken into the plant with the transpira- in anaerobic (low oxygen) conditions for plant tion stream (water), slow water movement can roots, eventually causing death. When large often lead to temporary calcium deficiencies, numbers of roots die, the plant is often unable to resulting in blossom end rot. take up sufficient nutrients, resulting in nutrient Management—Provide adequate calcium fer- deficiencies. Yellowed foliage due to flooding. tility and proper irrigation. Do not use high lev- Management—While damage from flooding els of ammonia fertilizer, which can aggravate is often unavoidable, planting in raised beds will this problem. Avoid root injury. improve drainage. 4 2. Drought stress. Cucurbits are particularly 4. Hollow heart is the formation of a hollow sensitive to drought. Fruit are typically 85% to cavity inside some cucurbit fruit. This disorder 90% water and can suffer under drought condi- can result from a number of factors, including tions. Pumpkins often produce long vines with low boron levels, genetics, and uneven water many leaves and can transpire large quanti- management. Although not outwardly visible, ties of water during hot summer days. Severe hollow heart makes fruit unmarketable. drought stress affects fruit development, result- Management—Avoid varieties with a tenden- ing in unmarketable produce. Affected cucumber cy to exhibit hollow heart. Ensure that boron lev- fruit may appear curled, distorted, or tapered els in the soil are adequate; however, be careful at the blossom end; pumpkins become soft and not to overfertilize. Follow recommended plant spacing, and avoid erratic irrigation. wrinkled. In addition, drought-stressed pump- Hollow heart of cucumber. 4 physiological and nutrient disorders 5 8 Nitrogen deficiency on pumpkin. 5. Magnesium deficiency is more likely to plant micronutrient, high levels of it can lead Magnesium deficiency on muskmelon leaves. occur on sandy soils with a low pH, especial- to toxicity symptoms in cucurbits. Manganese ly in dry years. Sandy soils often have a low toxicity is generally the result of a low soil pH, 6 cation exchange capacity and may not con- which allows manganese to become available to tain adequate levels of magnesium. Deficien- plants in toxic levels. cy symptoms are more commonly observed Management—Check the soil pH in the fall in muskmelon than in other cucurbits. Symp- prior to planting; if it is below 6.0, apply lime in toms first appear as a yellowing between the the fall and disk in. leaf veins (interveinal chlorosis), beginning on the oldest leaves and slowly spreading to newer 7. Molybdenum deficiency usually affects growth. Yellowed tissues may turn brown, die, muskmelons grown on dark heavy soils with a and drop out, giving the leaf a shot-hole pat- pH below 6.0. Heavy applications of ammonium tern. Magnesium deficiency usually appears dur- nitrate through the drip lines may lower the pH ing periods of rapid growth, when the fruit is in the plant root zone and contribute to either enlarging. manganese toxicity or molybdenum deficiency. Other cucurbits do not show symptoms under Manganese toxicity on a muskmelon leaf. Management—Maintain the soil pH near 6.5. Soil test results should show at least 200 lb of the same growing conditions. Molybdenum deficiency usually is seen in the crown leaves 7 magnesium/acre. Potential sources of preplant magnesium include magnesium oxide and dolo- about the time the plants begin to vine. Leaves mitic lime. If necessary, fertigate Epsom salts become pale green to slightly chlorotic between (magnesium sulfate) and magnesium oxide the veins. As symptoms progress, the leaf mar- through a drip irrigation system. Avoid heavy gins become necrotic and plant growth ceases. applications of fertilizers containing compet- Management—Maintain a soil pH between ing cations (K+, Ca++, NH4++). Foliar sprays 6.0 to 6.5; foliar treatments with sodium molyb- are generally ineffective in correcting significant date will help alleviate symptoms and permit deficiencies. normal growth 6. Manganese toxicity symptoms include 8. Nitrogen deficiency generally appears as water-soaked areas on the underside of leaves a yellowing of older foliage on plants. Nitro- and yellow or bronzed spots on the upper leaf gen is the most abundant nutrient in the plant Molybenum deficiency. surface. Although manganese is an essential and often the most limiting nutrient for plant 5 physiological and nutrient disorders 9a 9b Early (a) and severe (b) ozone injury to watermelon. growth. Cucurbits are not particularly heavy brown and gray areas that die and slough off. ly spaced, bees may have difficulty locating the nitrogen feeders but can experience nitrogen Severe damage can result in almost complete flowers. deficiencies during periods of rapid growth or defoliation of some plants. Ozone damage is Management—Provide pollinators to ensure fruit set. often mistaken for disease or spray injury. good fruit set and high yields. Do not spray Management—For cucurbit crops that are Management—Tolerance to ozone varies with insecticides during morning hours when flow- grown with drip tape and black plastic mulch, crop and variety. Seeded (diploid) watermelons ers are open and insects are actively pollinat- broadcast and disk in about 1⁄3 to 1⁄2 of the total tend to be more sensitive to ozone than seedless ing plants. nitrogen requirement for a season prior to form- (triploid) varieties. ing beds; fertigate the remainder through- 10 out the season.