91 articles tagged "Cucurbits".

Downy mildew of watermelon causes dark brown or black lesions often surrounded by a yellow halo.

This disease has been observed on watermelon in Knox County. The following article will discuss the symptoms, biology and management of downy mildew of cucurbits. Symptoms. The symptoms of downy mildew vary depending on the host.    On watermelon, the lesions start out as chlorotic (yellow) areas that become round and necrotic (brown/black) areas surrounded by a chlorotic halo. Lesions may be limited by veins (Figure 1). Note that leaf lesions of gummy stem blight may have dark fungal structures (pycnidia) present that are lacking with downy mildew. Also, whereas gummy stem blight will affect stems and petioles, downy mildew will not.  Pumpkin lesions also start out chlorotic and are often angular. Eventually, the chlorotic lesions become necrotic. Lesions may be more common along a vein. Lesions on muskmelon often have poorly defined margins and are not as angular as described above for pumpkin.   Cucumber lesions start out chlorotic and very[Read More…]

Magnesium deficiency in cantaloupe often occurs in high

​I have observed many fields of cantaloupes with magnesium deficiency or manganese toxicity. Watermelon plants may exhibit similar symptoms, but not as frequently as cantaloupe. Both disorders are related to acid (low pH) soils and usually occur in clusters in a field. Magnesium deficiency usually appears on sandy ridges and can be recognized by interveinal yellowing and death of tissues on older leaves (Figure 1). Manganese toxicity also first occurs on older leaves but appears in heavier or darker sands, often in low areas of the field. The diagnostic feature of manganese toxicity are the tiny pin-hole type lesions with yellow halos clustered between the veins (Figure 2). Leaves are best viewed when held up to the sun. These disorders can easily be confused with an infectious disease. In particular, magnesium deficiency has been confused with Alternaria leaf blight. Symptoms may seem to “spread” from areas of the lowest pH[Read More…]

​Populations of striped cucumber beetles continue to remain high. Muskmelon and cucumber growers should continue to monitor and spray as needed to avoid transmission of the pathogen that causes bacterial wilt of cucurbits. Wilt symptoms are showing up on melons throughout the state at this time, with greater prevalence in the southern counties and less further north. Growers are encouraged to spray as late in the day as possible, preferably after the flowers have closed and the bees have left the field, so that effects on pollinators are minimized.

​Growers may be wondering whether to replant pumpkin fields where the stand is uneven due to excess moisture. Potential yield of the replants is one thing it would be good to know. We have data on yield of pumpkins direct-seeded or transplanted in mid-July in northern Indiana. The trials were no-till planted into a harvested wheat field. Pumpkins were harvested in mid to late October. Yield of direct-seeded pumpkins ranged from 0 to 0.6 tons per acre for 8 varieties in 2004, and from 2.6 to 6.4 tons per acre for 5 varieties in 2005. Yield of transplanted pumpkins ranged from 2 to 8 tons per acre for 8 varieties in 2004 and from 4.4 to 9 tons per acre for 5 varieties in 2005. For comparison, typical yields at this site for an early- to mid-June planting date with conventional tillage range from 10 to 25 tons per acre.[Read More…]

These lesions may be covered with a white mold during moist conditions. (Photo by Dan Egel)

​Most growers first notice this disease when large, soft areas develop on mature watermelon fruit. These lesions can be several inches across and are often covered with a white mold. The lesions usually form first on the bottom of the fruit, close to where the fruit comes into contact with the soil. Further development of the disease often results in lesions on the top of the fruit as well (see Figure 1). Conditions that favor Phytophthora fruit rot include warm, rainy weather such as occurred recently over much of Indiana. Water that stands in pools also favors severe disease symptoms. Overhead irrigation may help the disease to spread. Phytophthora fruit rot can spread rapidly when conditions are favorable. The organism that causes Phytophthora fruit rot of watermelon is Phytophthora capsici. This organism is more closely related to algae than to fungi. Therefore, P. capsici is sometimes referred to as a fungus-like[Read More…]

​​A field day will be held on July 9 to share with the public the various research activities at the Southwest Purdue Agricultural Center in Vincennes, IN. The day will start at 7:30 A.M. with a health fair. Registration starts at 8:30 A.M. Presentation topics include: managing cucumber beetles while protecting bees, production of vegetables in high tunnels, canola production, hybrid cottonwood as a bioenergy crop, grape production, field crops disease update, soybean production, maximizing seed corn investment and benefits of starter fertilizer. Lunch is free with registration. A PARP class will be offered after lunch. Please contact Barb Joyner at 812-886-0198 or joynerb@purdue.edu to RSVP or go on-line at http:///tinyurl.com/2015SWPAC.

​So far it appears that populations of striped cucumber beetles appear to be low to moderate in most areas. The often cool and/or wet weather may be suppressing their activity currently, so be prepared if we get a period of warm, dry weather. Remember that cantaloupes and cucumbers are most susceptible to bacterial wilt, so the threshold for treatment is relatively low, 1 beetle/plant. For watermelons, pumpkins, and most squashes, the threshold is 5 beetles/plant because those cucurbits are less susceptible to bacterial wilt. When treating cucurbits that are in bloom for beetles, growers should wait to begin spraying until the flowers have closed up for the day. Ideally, sprays should be applied late in the evening if possible, because the potential for bee kills are reduced and that will allow for maximum residue levels on the foliage the next day.

​Striped cucumber beetles are emerging from their overwintering habitat in southern Indiana. This pest can damage cucurbit crops in several ways. One that I saw this week is that they can kill young transplants by their direct feeding. Of more critical concern usually is their ability to transmit the bacterium that causes bacterial wilt of cucurbits. Cantaloupes and cucumbers are especially susceptible to this disease. Pumpkins and some of the winter squashes are susceptible when the plants are young. Other squash and watermelons are not affected by the disease. Therefore, based on years of research and experience, we have set the treatment threshold at 1 beetle per plant for cantaloupes, cucumbers, and very young pumpkins and winter squash (less than 3 weeks old). For watermelons, summer squashes, and older pumpkins and winter squashes, the threshold is 5 beetles per plant.  Our research has shown that for cucurbits grown in the[Read More…]

​It’s early in the growing season, but I am already receiving calls about aphids on melons. We had lots of problems with aphids in 2013 and not very many last year. Particularly at this time of year, I’m recommending Assail® for aphid control on melons for several reasons. First, it does an excellent job killing aphids. Second, it will also provide very good control of striped cucumber beetles when they become active in your field. Third, I’ve never been a big fan of pyrethroid insecticides for control of aphids. They work to some extent but we have other products that are better. Finally, the active ingredient in Assail®, acetamiprid, is much less toxic to honey bees than the other neonicotinoid insecticides that could be used for aphid control. If you used either Admire Pro® or Platinum® at planting time, you should receive 3-4 weeks of aphid control. Growers should be[Read More…]

​I have received calls about seedcorn maggots in melons and have seen wireworm damage in my research plots in Vincennes. Seedcorn maggots are usually associated with cool weather since the adult flies will not lay their eggs near melons plants when the soil temperature exceeds 70°F. So the cool weather we have had this past week could promote seedcorn maggot problems. One of the species of wireworms I observed is Conoderus lividus, a species commonly associated with corn. If you are planting melons after corn, the field could be infested with wireworms, although frankly this is fairly rare. You can determine the potential for wireworm problems prior to planting by burying a cup of flour or untreated grain (corn or wheat) about 6 inches under the ground. Come back and dig up the bait in about a week and look for wireworms. About the only product melon growers have available[Read More…]

Vegetable Crops Hotline - Department of Horticulture and Landscape Architecture 625 Agriculture Mall Dr. West Lafayette, IN 47907

© 2018 Purdue University | An equal access/equal opportunity university | Copyright Complaints | Maintained by Vegetable Crops Hotline

If you have trouble accessing this page because of a disability, please contact Vegetable Crops Hotline at guan40@purdue.edu.