Posts Tagged ‘winter squash’

Pollination Disorders in Cucurbits

Thursday, July 12th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Watermelon harvest is underway on Delmarva; cantaloupe harvest started early this year, squash and cucumbers have been producing for over a month; and pumpkins and winter squash are setting fruit in earlier plantings. Each year, we see pollination problems with vine crop fruits, especially when weather conditions are unfavorable.

Signs of incomplete pollination in cucurbits include bottlenecked fruit or fruit with a pinched end, crooked or lopsided fruit, fruit small in size or nub-like; and fruits with prominent lobes or that are triangular in shape. Causes of incomplete pollination may be inadequate pollen transfer by pollinating insects; inadequate pollen sources (pollenizers); or hot, dry weather that reduces pollen viability or that desiccates flower parts during pollination. Research has shown that a minimum of 1,000 grains of pollen are required to be distributed over the three lobes of the stigma of the female flower of a watermelon to produce a uniformly shaped fruit.

Hollow cavities in fruit and vacant seed cavities are related to lack of seed formation, again traced back to poor pollination. Fruit tissue separation, such as hollow heart in watermelon, may also be due to inadequate pollination and may be worsened by rapid fluctuation in environmental conditions affecting fruit development.

Leaf Aging in Cucurbits

Friday, June 22nd, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

We are starting to see the oldest leaves (crown leaves) in watermelons, cantaloupes, squash, cucumbers, and pumpkins with large areas that are discolored (white, tan, or bronze). These leaves will be brittle to the touch and may start to tear or shred with high winds and storms. This condition is common in cucurbit crops and can be due to a number of leaf aging factors including mineral nutrient scavenging (export of mobile nutrients from oldest leaves to newer leaves), ozone air pollution damage, chemical phytotoxicity, repeated stress cycles, and wind injury. Leaf cells that die will leak their contents, releasing enzymes and oxidizing chemicals affecting nearby cells thus accelerating the “aging” process. This results in large patches of dead leaf cells that then dry, making the leaf feel brittle. If leaf veins are damaged, water and food transport will be compromised, accelerating leaf decline. This leaf aging is not to be confused with damage from mite feeding which is also concentrated on oldest leaves.

Cucurbit Downy Mildew Alert!

Friday, June 15th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Cucurbit downy mildew was confirmed in Dorchester and Caroline counties in Maryland on June 12. Symptoms first appeared on June 8. This downy mildew occurrence is one month earlier than any occurrence in recent years. Growers should scout aggressively for this disease on cucumber and other cucurbits. This disease is favored by cool, humid weather including cool dewy nights. Weather during June 12-14 is forecast to be conducive to further spread. Tank-mix Ranman or Previcur Flex with a protectant fungicide and alternate sprays with a material with a different mode of action. Be careful not to rely on one fungicide class. Use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program. Presidio, which was commonly used in previous years, was not as effective as expected in 2011 University trials.

Downy mildew on the lower surface of a cucumber leaf. Notice the angular, water soaked lesions on this newly infected leaf. (Image courtesy of Bugwood and Gerald Holmes)

Consult the Commercial Vegetable Production Recommendations for further information on resistance management and available fungicides (in Maryland, Extension Bulletin 236 and in Delaware, Extension Bulletin 137). Because downy mildew has only been found on cucumber, targeted sprays on other cucurbits crops such as pumpkin, squash, watermelon, etc. are not necessary, at this time. Instead scout these crops aggressively and continue to apply a broad-spectrum spray program.

Watch for Striped Cucumber Beetle and Squash Bugs at Base of Cucurbit Plants

Friday, June 8th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu

I talk about this every year it seems, but I still see cucumber beetle and squash bug problems at the base of growers’ cucurbit plants. So far this has been a ‘good’ year for striped cucumber beetle and squash bug populations in just about every cucurbit field. Some fields have been hit particularly hard with beetles causing 5-10% plant loss due just to their feeding. The biggest problem with these pests, and why control sprays have not worked well, is that they are consistently hiding at the base of the plant where they are feeding on the stem. Most of the time we look for the foliage damage to tell us how well our spray program is working. Sprayers are set up usually to cover a lot of leaf canopy and do not do a very good job of putting chemical along the base of the stem. This stem feeding can be severe enough on small plants that either pest alone could cause some wilting, but with both feeding on this relatively small area of the stem they are causing considerable damage (Fig. 1). Even on larger plants the feeding can still cause significant damage (Fig. 2). It is hard enough to kill squash bug adults with a good cover spray, but when only small amounts of spray are reaching them on the lower stem they will not be controlled. Often it is possible to walk by plants and even inspect them and still see no beetles or squash bugs, as they will stay down at the base of the plant and only move when the base is exposed. In a couple fields about 10% of the plants were wilting (Fig. 3) due to squash bug and cucumber beetle feeding. These pictures are from a squash field but the same problem is occurring in watermelon and cantaloupe fields with both striped cucumber beetles and squash bugs feeding at the base of a plant. Growers need to check to see if this type of feeding is occurring in their fields and if so insecticide applications (pyrethroids such as Asana, Warrior, etc.) must be directed at the base of the plant.

Figure 1. Striped cucumber beetle feeding damage at base of a small squash plant

 

Figure 2. Larger cucurbit plant with feeding at its base by cucumber beetle

Figure 3. Wilted squash plant due to squash bug and cucumber beetle feeding at its base

Cucurbit Downy Mildew Fungicide Decisions

Friday, May 11th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew on cucurbits has been a problem on Delmarva beginning in early July for the last few years. Good fungicides for management are available. However, last year in my trials, one of these fungicides, Presidio, was not as effective as expected. Looking ahead to your spray program, be careful not to rely on one fungicide class. It is difficult to know which fungicides will be effective here, because our population does not overwinter and is reintroduced from the South each year. Therefore use excellent resistance management practices to avoid allowing the pathogen to develop resistance and to improve the efficacy of your fungicide management program.

Fungicide Resistance management guidelines by crop are available online http://mdvegdisease.umd.edu/Disease%20Management/Fungicide.cfm and hard copies are available in Delaware at the county Extension offices.

Cucurbit Downy Mildew Update – August 19, 2011

Friday, August 19th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

There were reports of downy mildew on pumpkin in northern New Jersey at the beginning of the week. This was sent to the WCU mailing list to make you aware that downy mildew was beginning to appear on more than just pickling cucumber in the area. With the recent thunderstorms, cooler nights and morning fog, conditions will be more favorable for disease development. Maintain your fungicide program at this time. Growers should be aware that the fungicides that have been the most effective on downy mildew on cucumber (namely Presidio, Ranman, and Previcur Flex) will also be very effective on pumpkin, cantaloupe and any other cucurbit. Tanos and Curzate could be added to that list as well for cucurbits other than cucumber. Be aware that Presidio has some plant back restrictions for crops not on the label. The link will take you the new supplemental label: http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2011/08/PresidioSupplementalLabel.pdf. Wheat can be planted 30 days after treatment. This was added in the supplemental label.

Gavel 75DF from Gowan Company LLC Now Labeled for Pumpkin and Winter Squash

Thursday, August 4th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Gavel has been labeled for use on pumpkin and winter squash for the control of Alternaria leaf spot, Cercospora leaf spot, downy mildew and Phytophthora fruit and stem rot. This is in addition to labels for use on cucumber, cantaloupe, summer squash and watermelon. Gavel is not recommended for downy mildew control on cucumbers but is recommended for control on pumpkin and winter squash as well as watermelon and cantaloupe. Remember that Gavel contains mancozeb, so some cantaloupe varieties might be sensitive. Go to http://www.cdms.net/LDat/ld4PP006.pdf to see updated label.

Controlling Powdery Mildew in Cucurbits

Friday, July 8th, 2011

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Powdery mildew is a problem on cucurbits each year. All cucurbits are susceptible, however host plant resistance in many cucumber and cantaloupe cultivars has successfully managed the problem. Susceptible varieties as well as other crops like pumpkin and squash are hit hard by powdery mildew. Disease builds up during July and becomes severe in August and September. Powdery mildew is a challenge to manage, especially in hot dry conditions. Also, there is resistance in the powdery mildew pathogen to many of our fungicides such as Quadris. Therefore, fungicides must be chosen carefully.

To manage powdery mildew, select cultivars (varieties) with resistance or tolerance. Even a moderate level of resistance will improve the efficacy of a fungicide spray (and help reduce the damage if you miss a spray). Scout the field and apply the first powdery mildew spray when you see one lesion on the underside of 45 old leaves.

Always follow good resistance management guidelines. 1) Keep on a good spray schedule (a 7-day interval for powdery mildew). 2) Apply fungicides at label rate (don’t cut the rate). 3) Be sure you are getting good fungicide coverage of your plants. 4) Be aware of products that are at risk for resistance development. 5) Materials with different modes of action (FRAC codes) should always be alternated. 6) Late in the season when powdery mildew has become well established, only apply protectant fungicides such as chlorothalonil or sulfur.

Below are the fungicide programs suggested for the various crops.

Summer Squash or Cucumber: Alternate a tank mix that contains chlorothalonil and either Procure, Rally, Folicur, or Inspire Super, with a tank mix containing Pristine plus chlorothalonil.

Muskmelon: Alternate Quintec plus chlorothalonil, with a tank mix containing chlorothalonil and either Procure, Rally, Folicur, or Inspire Super.

Extensive white sporulation of powdery mildew on pumpkin leaves.

Pumpkin: Alternate Quintec plus chlorothalonil with a tank mix containing chlorothalonil and either Pristine, Procure, Rally, Folicur, or Inspire Super. An alternative and less expensive option is to alternate Micronized Wettable Sulfur with one of the above options. Sulfur may injure plants, especially at high temperatures, which is why it is only recommended for pumpkin. Certain varieties can be more sensitive.

 

Cucurbit Downy Mildew Alert – July 1, 2011

Friday, July 1st, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu and Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland; keverts@umd.edu

Downy mildew was confirmed on seeded cucumbers in Cumberland County, NJ near the city of Vineland. There were no reported downy mildew infections on any transplanted cucurbits in this area. This is the first report of downy mildew on cucurbits in the Mid-Atlantic region this year. Downy mildew has also been increasing in North Carolina the last several weeks. This is a very long leap from NC to NJ if this infection was from air transported spores. Traditionally we can expect downy mildew to arrive here sometime around the 4th of July. DE and MD have sentinel plots for monitoring downy mildew on cucurbits and have been negative for downy so far. These are scouted regularly in addition to reports and samples that we receive from the field. Hopefully we can provide an early warning when it appears here so that timely fungicide applications with downy mildew specific fungicides can be made.

What growers should do:

● Now that downy mildew has been detected in the region growers should be scouting on a daily basis.

● In areas where rainfall has occurred, growers may want to apply targeted fungicides to cucumbers. Tank- mix Presidio, Ranman, or Previcur Flex with a protectant fungicide and alternate sprays with a material with a different mode of action. Because downy mildew has only been found in adjacent states on cucumber, targeted sprays on other cucurbits crops (pumpkin, squash, watermelon, etc.) are not necessary, at this time. Instead scout aggressively and continue a broad-spectrum spray program.

● All abandoned cucumber and summer squash fields should be sprayed with gramoxone or disced under immediately after last harvest to kill the foliage! Abandoned fields left unattended after use will only serve as a source of inoculum for other fields once downy mildew makes its way into our area.

● Please see the 2011 Commercial Vegetable Recommendations Guide for specific fungicide recommendations

● To track the progress of cucurbit downy mildew in the eastern US and to keep up with reports of Downy mildew from other states please visit North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at http://cdm.ipmpipe.org/

 

Phytophthora Fruit Rot on Cucurbits

Friday, June 24th, 2011

Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu

Conditions have not been very favorable for fruit rot lately but we always seem to run the risk of scattered thunderstorms and frog-strangling rain events at this time of the year. Phytophthora blight is a tough disease to control, but if you have cucurbits in fields that had fruit rot in the past you are at very high risk if the soil stays saturated even for a few hours. This is a fungus that moves in water and the spores will move where water goes. (Spores will not move more than a few feet in the air.) Some additional cultural controls would be rotation (5 years or more) for watermelons, sub-soiling between the rows before they close to help water drain faster and to keep the fruit out of standing water. Fungicides will only suppress the disease and those that have the best activity are the following: Presidio, Revus, Ranman plus a surfactant (see label), Forum, Gavel and Tanos. Depending on the test, the season, and the location, the efficacy of these fungicides varies. However, proper application of these products will result in better yields than in untreated fields. Remember that Revus and Forum are Group 40 fungicides and have the same mode of action, so they should not be applied in succession. All of these fungicides except Ranman should be tank mixed with fixed copper if the label allows. Fixed copper is not compatible with Ranman plus the surfactant. Good coverage of fruit is very important. For more information on fungicides check the 2011 Commercial Vegetable Production Recommendations.