Posts Tagged ‘cucumber’

Striped Cucumber Beetle Populations Still Very High

Friday, July 27th, 2012

Jerry Brust, IPM Vegetable Specialist, University of Maryland; and Karen Rane, Extension Specialist Entomology, University of Maryland

We have seen very high populations of striped cucumber beetles on squash, pumpkins, cantaloupe, watermelon and other cucurbits over the last few weeks. These populations at times have reached over 20-30 beetles per plant. If a spray was missed or plants were not thoroughly covered with an insecticide application the beetles would soon consume that unprotected area very rapidly (Fig. 1). This area is often times the base of the plant. This is especially true if the cucurbits are sprayed with an air-blast sprayer. While air-blast sprayers do a good job of covering leaves with material, they often do not do a great job of covering the base of a plant and heavy feeding can occur (Fig. 2). The feeding can lead to plants being girdled by beetles or can lead to bacterial wilt infection—even though the leaves of the plant show almost no feeding. This feeding by the beetles also opens the base of the stem to infection from soil organisms and greater rates of Fusarium and bacterial soft rots are possible. When beetle populations are this high the base of the plant, even more so than the foliage, needs to be protected from heavy feeding.

Figure 1. Two squash leaves fed upon heavily by striped cucumber beetles because of the lack of good spray coverage.

Figure 2. Base of pumpkin plants damaged by striped cucumber beetles due to poor spray coverage

Pollination Disorders in Cucurbits

Thursday, July 12th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

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.

Sunburn in Fruits and Fruiting Vegetables

Friday, July 6th, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

High temperatures, clear skies and high light radiation, and long daylengths are a recipe for developing sunburn in fruits and fruiting vegetables. We commonly see sunburn in watermelons, tomatoes, peppers, eggplants, cucumbers, apples, strawberries, and brambles (raspberries and blackberries).

There are three types of sunburn which may have effects on the fruit. The first, sunburn necrosis, is where skin, peel, or fruit tissue dies on the sun exposed side of the fruit. Cell membrane integrity is lost in this type of sunburn and cells start leaking their contents. The critical fruit tissue temperature for sunburn necrosis varies with type of fruit. For cucumbers research has shown that the fruit skin temperature threshold for sunburn necrosis is 100 to 104°F; for peppers, the threshold is 105 to 108°F, and for apples the critical fruit skin temperature is 125-127 °F. Fruits with sunburn necrosis are not marketable.

The second type of sunburn injury is sunburn browning. This sunburn does not cause tissue death but does cause loss of pigmentation resulting in a yellow, bronze, or brown spot on the sun exposed side of the fruit. Cells remain alive, cell membranes retain their integrity, cells do not leak, but pigments such as chlorophyll, carotenes, and xanthophylls are denatured or destroyed. This type of sunburn browning occurs at a temperature about 5°F lower than sunburn necrosis (115 to 120° F in apples). Light is required for sunburn browning. Fruits may be marketable but will be a lower grade.

The third type of sunburn is photooxidative sunburn. This is where shaded fruit are suddenly exposed to sunlight as might occur with late pruning, after storms where leaf cover is suddenly lost, or when vines are turned in drive rows. In this type of sunburn, the fruits will become photobleached by the excess light because the fruit is not acclimatized to high light levels, and fruit tissue will die. This bleaching will occur at much lower fruit temperatures than the other types of sunburn.

Genetics also play a role in sunburn and some varieties are more susceptible to sunburn. Varieties with darker colored fruit, those with more open canopies, and those with more open fruit clusters have higher risk of sunburn. Some varieties have other genetic properties that predispose them to sunburn, for example, some blackberries are more susceptible to fruit damage from UV light.

Control of sunburn in fruits starts with developing good leaf cover in the canopy to shade the fruit. Fruits most susceptible to sunburn will be those that are most exposed, especially those that are not shaded in the afternoon. Anything that reduces canopy cover will increase sunburn, such as foliar diseases, wilting due to inadequate irrigation, and excessive or late pruning. Physiological leaf roll, common in some solanaceous crops such as tomato, can also increase sunburn.

In crops with large percentages of exposed fruits at risk of sunburn, fruits can be protected by artificial shading using shade cloth (10-30% shade). However, this is not practical for large acreages. For sunburn protection at a field scale, use of film spray-on materials can reduce or eliminate sunburn. Many of these materials are Kaolin clay based and leave a white particle film on the fruit (such as Surround, Screen Duo, and many others). There are also film products that protect fruits from sunburn but do not leave a white residue, such as Raynox. Apply these materials at the manufacturer’s rates for sunburn protection. They may have to be reapplied after heavy rains or multiple overhead irrigation events.

Leaf Aging in Cucurbits

Friday, June 22nd, 2012

Gordon Johnson, Extension Vegetable & Fruit Specialist;

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.

Cucumber Downy Mildew Update – June 22, 2012

Friday, June 22nd, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Downy mildew was confirmed on cucumber in Sussex County, Delaware this week. It was also confirmed on cucumber in the New Castle County CDM sentinel plot in Newark on Friday, June 22.  Continue with a good preventative program. The hotter weather is not as conducive to disease development.

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;

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 Found in New Jersey

Friday, June 1st, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

Cucumber downy mildew was confirmed in Gloucester County, NJ on May 30 and reports of CDM from North Carolina are increasing. Cucumber growers are encouraged to apply preventative fungicides immediately and scout their crop for symptoms of disease. The progress of the disease can be monitored online at North Carolina State University’s Cucurbit Downy Mildew Forecasting Center at

Cucurbit Downy Mildew Fungicide Decisions

Friday, May 11th, 2012

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

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 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;

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: Wheat can be planted 30 days after treatment. This was added in the supplemental label.

Controlling Powdery Mildew in Cucurbits

Friday, July 8th, 2011

Kate Everts, Vegetable Pathologist, University of Delaware and University of Maryland;

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.