Posts Tagged ‘muskmelon’

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.


Air Pollution in Vegetables

Friday, June 24th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

We are starting to see evidence of air pollution damage in sensitive vegetable plants. Those vegetables most susceptible include potatoes, watermelons, cantaloupes, snap beans, pumpkins, and squash.

Damage is most common during hot, humid, hazy weather with little wind. Air inversions, when warm air at the surface is trapped by even hotter air in the atmosphere above, lead to build up of air pollutants that cannot disperse and, consequently, plant injury. The most common form of air pollution injury to plants is ozone damage. Ozone is a strong oxidant and is formed by the action of sunlight on products of fuel combustion. It is moved from areas of high concentration (cities, heavy traffic areas) to nearby fields.

Ozone injury in susceptible vegetable varieties develops when ozone levels are over 80 ppb for four or five consecutive hours, or 70 ppb for a day or two when vegetable foliage at a susceptible stage of growth. Because it occurs in areas with high levels of automobile exhausts, crop injury is often visible on fields in close proximity to roads, especially with heavy summer weekend traffic. High pollution indexes in Baltimore and Washington are also a good indication that ozone damage may occur.

In potatoes, symptoms of ozone damage occur on the most recently emerged leaves and can be seen as a black flecking. Early red varieties are most susceptible.

Injury on watermelon leaves consists of premature chlorosis (yellowing) on older leaves. Leaves subsequently develop brown or black spots with white patches. Watermelons are generally more susceptible than other cucurbits to ozone damage. Damage is more prevalent when fruits are maturing or when plants are under stress. Injury is seen on crown leaves first and then progresses outward. Seedless watermelon varieties tend to be more resistant to air pollution injury than seeded varieties, so injury often shows up on the pollenizer plants first. “Ice box” types are the most susceptible.

Ozone injury on watermelon

In muskmelons and other melons, the upper surface of leaves goes directly from yellow to a bleached white appearance.

Ozone injury on squash and pumpkins is intermediate between watermelon and cantaloupe starting with yellowing of older interior or crown leaves. These leaves subsequently turn a bleached white color with veins often remaining green.

In snap and lima beans, ozone causes small bleached spots giving a bronze appearance on upper leaf surfaces and pods. Leaves may ultimately turn chlorotic and senesce (drop).

Ozone injury can be easily misdiagnosed as mite injury, pesticide phytotoxicity, or deficiencies.

The key to avoiding air pollution injury is to plant varieties that are of low susceptibility and to limit plant stresses. Certain fungicides such as thiophanate methyl (Topsin and others) offer some protection against ozone damage.


Early Transplanting of Warm Season Vegetables

Thursday, April 14th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist;

Earliest plantings of watermelons, cantaloupes, summer squash, and tomatoes will begin in the next 10 days. First transplanting of crops such as peppers and eggplant will begin in early May. One of the characteristics that all of these crops have in common is that they are warm season vegetables that are sensitive to cold temperatures, both in the root zone and above ground. There has been a tendency to risk earlier and earlier plantings as growers try to hit the early market. Over the years, many of our early plantings of summer vegetables have suffered because of early cold damage and inadequate provisions to protect plants.

For early transplanted warm season vegetables choose the lightest ground that warms up quickly. Plant higher sections in the field first. Avoid areas that receive any shade from woods or hedgerows. Early fields should be protected from extreme wind and should not have frost pockets. Rye windbreaks planted between each bed are desirable for early plantings because they limit heat transfer by wind. If no rye windbreaks have been planted, then consideration should be given to using row covers to protect the plants – either clear slitted or perforated low tunnels or floating row covers. Even where windbreaks have been used, row covers may be necessary for extremely early plantings.

Lay plastic mulch well ahead of time to warm soil. Black plastic mulch should have excellent soil contact. Firm beds and tight mulch are much more effective in warming soils. Make sure that there is good soil moisture when forming beds and laying plastic because soil water will serve as the heat reservoir during cold nights.

When producing transplants, use larger cell sizes and grow plants so that they have well developed roots in those cells for the first plantings. Large cell sizes will perform better than small cells in early plantings. Careful attention needs to be paid to hardening off warm season vegetable transplants that will be planted early. Gradual acclimation to colder temperatures will reduce transplant shock. Do not transplant tender, leggy plants or plants coming directly out of warm greenhouse conditions for these early plantings.

Watch extended weather forecasts and plant at the beginning of a predicted warming trend. Monitor soil temperatures in plastic beds and do not plant if they are below 60°F. Soil temperature in beds should be measured at the beginning of the day when at the coolest. When soil temperature conditions are not favorable, wait to plant. Avoid planting in extended cloudy periods, especially if plants have come out of the greenhouse after an overcast period. These plants will not perform well. Extra caution should be taken to minimize root injury during transplanting. When transplanting, make sure that there is good root to soil contact and there are few air pockets around roots.

In years with cold, cloudy, windy weather after transplanting, we have had large losses of transplants in the field. It is critical to have warm soil conditions after transplanting to allow roots to grow out into the bed quickly. In cold, cloudy conditions, plants shut down physiologically, little root growth occurs, and the existing roots on the transplant do not function well. If there is any wind, plants lose more water than they can take up and they die due to desiccation. This is accelerated when the sun does come out – the first sunny day after an extended cold, cloudy period is when you will see the most wilting of weakened transplants.

If cold weather occurs after transplanting, warm season vegetables vary in their ability to tolerate adverse weather after being set out. Tomatoes will stop growth but will grow out without much damage once warm weather returns. Summer squash and cucumber transplants may be temporarily stunted but generally grow out of the condition. Watermelons will hold if they have been hardened off properly. Cantaloupes can be stunted if exposed to excessively harsh early conditions. Peppers and eggplants will not put on any root growth until temperatures are warm enough. If stunting occurs on any of these warm season vegetables, you may lose the early advantage you were seeking. In addition, remember that all of these vegetables are susceptible to frost damage and will be killed by a late freeze.


Powdery Mildew and Alternaria on Cantaloupe

Friday, July 23rd, 2010

Bob Mulrooney, Extension Plant Pathologist;

Powdery mildew is beginning to get established on cantaloupes now. Include fungicides for powdery in your spray programs. See the article titled ‘Powdery Mildew on Cucurbits’ in WCU 18:15 for more information.


Powdery mildew on cantaloupe

Alternaria leaf blight is not widely seen anymore because many of our hybrid cultivars have differing levels of resistance and growers keep good spray schedules. I could not help showing you what it looks like if you should run across it and wonder what that leaf spot looks like. It was seen on an old variety ‘Hales Best Jumbo’. Control is provided by alternating Bravo (chlorothalonil) or mancozeb with Pristine or alternating Bravo with a tank mix of Bravo plus Quadris, Cabrio or Reason.


Alternaria leaf blight on ‘Hales Best Jumbo’

Viruses and Other Problems Found in Watermelon and Cantaloupe in Central Maryland

Friday, July 9th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

Cucumber mosaic virus (CMV) has been found in some watermelon fields in central Maryland. CMV is not uncommon in the NE United States, but in a two-year survey of pumpkin that Kate Everts, Karen Rane, Mark VanGessel and I did in Maryland and Delaware we did not detect CMV in any pumpkin field we sampled. CMV is transmitted primarily by aphids, but also by cucumber beetles, mechanically and to a lesser extent in seed. Many species of aphid can vector the virus in a non-persistent manner – the most common species in Maryland are: Melon aphid Aphis gossypii and Green peach aphid Myzus persicae. The virus is acquired by aphids within 10 seconds after they begin to probe an infected plant. The virus can be transmitted to other plants by aphids in less than one minute. This is why insecticides do not stop initial infections. Aphids lose the ability to transmit CMV after about 2 minutes and completely lose the ability after 2 hours. There are many strains or types of CMV, some isolates can lose their transmissibility by one aphid species but retain their transmissibility with another. In one field I visited there were many early season striped cucumber beetles and I think they may have been responsible for transmitting the virus from weeds to the watermelon in this field. The virus symptoms were first seen a few weeks ago – very early in the season for us to be seeing virus symptoms in watermelon fields. Some of this may be due to early season cucumber beetles transmitting the virus and some may be due to the extreme heat and drought we are experiencing. The drought is causing weeds to wither and the aphids that are present on them are moving earlier than they normally would to greener fields—like our well cared-for cucurbit fields.

The symptoms I have seen on watermelon are rather non-descript (Fig. 1) and look like they could be due to many things, including herbicide injury. Leaves of new growth are crinkled and deformed with a slight yellowing to them. CMV produces a systemic infection in most host plants with the older plant tissues that developed before infection rarely being affected by the virus. Tissues that develop after infection are affected to varying degrees. The concentration of the virus increases for several days following inoculation, and then decreases until it levels off. While there is transmission through seed in 20 host species, the most important source of virus may be weeds, which allow for overwintering of the virus. In addition to seeds, CMV overwinters in many perennial weeds and some crop plants. The perennial weeds wild ground cherry, horse nettle, milkweed, ragweed, pokeweed, nightshade, and various mints can harbor the virus in their roots, and in the spring the virus migrates to new growth, which aphids then transmit to susceptible crop plants. CMV is easily transferable through sap carried on the hands, clothes and tools of people harvesting fruit, weeding or turning vines in a watermelon field.

Figure 1. New growth on watermelon with CMV symptoms

There are some CMV resistant (tolerant) cucumber varieties available that produce a good crop, but most other cucurbits are susceptible to CMV. Using reflective mulch reduces the early season infection from aphids and gives an additional 2-4 weeks of a virus-free cucurbit field. Once the plants cover the plastic the reflective mulch ceases to be an effective deterrent. Pesticides only work to reduce the in-field spread of aphids and therefore, CMV and other viruses.

I have also seen virus symptoms in cantaloupe recently. Leaves are mottled and puckered (Fig. 2), and symptomatic tissue tested positive in a generic potyvirus test. Initial tests for the common potyviruses Watermelon Mosaic Virus, Zucchini Yellow Mosaic Virus and Papaya Ringspot Virus were negative for these cantaloupe leaves. Additional tests are being performed to try to identify which specific potyvirus is affecting the cantaloupe.

Figure 2. Cantaloupe with potyvirus symptoms

In addition to the virus problems, I have seen, especially in the last two weeks, a great increase of necrotic spot appearing on the crown leaves of watermelon plants (Fig. 3). This is being caused by a combination of air pollution problems-hot humid air not moving much and the fact that the plant takes nutrients from the crown leaves when there is a heavy demand from the growing fruit. This results in the crown leaves turning brown and eventually breaking down. In cantaloupe I have seen some leaf marginal chlorosis (yellowing of leaf margins) of some leaves (Fig. 4). This is often caused by salt deposits (from foliar nutrient or pesticide sprays) that accumulate around leaf margins, which have a toxic effect on the gas exchange pores (hydathodes) located at leaf tips. This is commonly seen under high temperature and humidity.

Figure 3. Necrotic spots on watermelon crown leaf

Figure 4. Marginal chlorosis of cantaloupe leaf

Vegetable Disease Update – July 2, 2010

Friday, July 2nd, 2010

Bob Mulrooney, Extension Plant Pathologist;

Cucurbit Downy Mildew
We are at minimal risk at the present but keep up to date by checking the ipm PIPE website regularly for updates. Downy mildew was found in New York state for the first time on cucumber in Erie and Niagara counties close to the Ontario, Canada infection site. The northern march of downy has been slowed. We have had some weather patterns coming north but the clear skies and plenty of UV radiation have probably been keeping viable spore number low. We are checking our sentinel plots weekly for downy mildew here in DE.

Bacterial Wilt
Bacterial wilt on slicing cucumbers was diagnosed this week. Symptoms on this planting were random wilting of several runners on 20% of the plants. Sticky strands of bacterial ooze can be seen when the cut ends of the wilted runners are touched together then slowly drawn apart. Striped and spotted cucumber beetles carry the bacteria on their mouthparts and inoculate them when they feed on the succulent stems early in the season. Bacterial wilt is not seed borne and does not persist in the soil more than 2-3 months. It is thought that the bacteria acquire the bacteria from infected weed or volunteer cucurbit hosts. Cucumber beetle control is the primary control method.

Strands of bacterial ooze from touching cut ends of infected runner and pulling them apart slowly

Potato and Tomato Late Blight Webinar for Home Gardeners
Rutgers, Penn State and Cornell University vegetable plant pathologists will be holding a Webinar on Potato and Tomato Late Blight for home gardeners on July 13, 2010 at 6:30 PM. You are encouraged to participate in this timely topic. The linked announcement has all the information to enroll. It will be a good review for commercial producers as well.

Pythium Blight or Cottony Leak on Snap Beans
Pythium blight or cottony leak on snap beans was diagnosed early this week. This disease likes the hot, humid conditions that we had before this recent break in the weather. When we go back to the humid weather again with scattered showers and irrigation this disease can be a threat. Look for the cottony white growth in the lower canopy and on pods close to the ground. There is a 24c registration for Ridomil Gold Copper (2 lbs/A) for prevention of Pythium blight in DE, MD and VA. Several applications may be necessary if favorable weather persists.

Cucurbit Powdery Mildew
Powdery mildew on cucurbits has been reported in New Jersey. Delaware growers should be scouting and begin applying fungicides for powdery mildew once 1 old leaf in 45 has been found with powdery mildew. See the article titled Powdery Mildew on Cucurbits in WCU 18:15 for suggested fungicides.

Powdery Mildew on Cucurbits

Friday, June 25th, 2010

Bob Mulrooney, Extension Plant Pathologist;

Continue to scout cucurbits for powdery mildew. Symptoms typically begin on older, lower leaves and can spread rapidly under dry, humid conditions. Control of powdery mildew begins with regular scouting for symptoms and weekly fungicide applications. Begin a fungicide program when one lesion is found on the underside of 45 leaves. For control of cucurbit powdery mildew in:

Pumpkin and Winter Squash:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With one of the following:
Micronized Wettable Sulfur (M2) at 4.0 lb 80W/A (Sulfur may injure plants especially at high temperatures. Certain varieties can be more sensitive. Consult label for precautions.)
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A
Quintec (quinoxyfen, 13) at 6.0 oz 2.08F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

When Powdery mildew has become well established in the mid- to late part of the season, only apply protectant fungicides such as chlorothalonil or sulfur.

Summer Squash and Cucumber:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With a tank mix containing:
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A

Muskmelon and Watermelon:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
Folicur (tebuconazole, 3) at 4.0 to 6.0 fl. oz 3.6F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A

With a tank mix containing:
Quintec (quinoxyfen, 13) at 6.0 oz 2.08F/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A

For more information on control of powdery mildew of cucurbits please see the 2010 Delaware Commercial Vegetable Production Recommendations Guide.

Seedcorn Maggot Damage in Early Planted Cucurbit Fields

Thursday, April 29th, 2010

Jerry Brust, IPM Vegetable Specialist, University of Maryland;

There have been several reports throughout Maryland of early planted watermelon and cantaloupe fields with seedcorn maggot (SCM) damage. The damage to transplants is often thought to be just damping-off or some other soil disease, but growers need to split the stems of the plants to see if they contain any seedcorn maggots. Stems can contain 12-45 maggots. The stem often looks whole above ground level, but below ground the stem and roots are often shredded (Fig. 1). The seedcorn maggot is an early season pest of many different crops. Most of these crops are direct seeded, but transplants are also attacked. It is more of a problem during damp, cool periods and in fields with manure or decaying residue. This year has been perfect for the fly to cause damage as we had a very early warm up followed by a cool down. This caused growers to start earlier and it also caused more of the pest population to become active early.

The seedcorn maggot is a pale, yellowish-white maggot found burrowing into seeds or transplants. Full grown maggots are legless, about 1/4 inch long, cylindrical, narrow and tapered. Maggots lack heads and legs, but have small black mouth hooks in front (Fig. 2).

The seedcorn maggot spends the winter as a larva inside a puparium in the soil. When mature, maggots pupate and emerge in April and May, mate, and lay eggs on moist soil high in organic matter, near decaying vegetation or at the base of transplants. The adult, which resembles a small house fly, is a gray to brown fly about 1/5 inch long that can be seen flying over freshly worked soil or where manure has been spread.

Seedcorn maggot eggs hatch a few days after being laid, and small, white, tapered maggots begin to feed on and burrow into plants or seeds. The maggots usually feed for 2 to 3 weeks before pupating in the soil. Adults emerge from the pupal case in about 7 to 14 days, mate, and begin a new cycle. The entire life cycle is as quick as 21 days, resulting in 3 or more generations each year.

There are no rescue treatments for infested plants. Fumigation and soil insecticides do not do a very good job of reducing SCM infestations since the maggots attack the seedling just below soil level. Even the use of systemic insecticides does not completely control maggot infestation s if the weather is cool and damp. The best control is a warmed soil. My research has shown that when temperatures reach 71oF at a 4 inch depth under BLACK PLASTIC, flies will stop laying eggs and larvae do not survive well. Row covers over the newly set transplants will also work to keep flies from laying eggs in the transplants.


Figure. 1 Transplant damaged by seedcorn maggot


Figure. 2 Maggots inside split stem of cantaloupe transplant

Downy Mildew on Cucurbits – August 21, 2009

Friday, August 21st, 2009

Bob Mulrooney, Extension Plant Pathologist;

The weather continues to be very favorable for downy mildew. It is spreading now to hosts other than cucumber. Cantaloupe, watermelon, winter squash and pumpkin have all been infected in the region. The spots are much smaller on butternut squash and watermelon but still produce the small tuft of fungus growth on the underside of the leaf. All cucurbit growers need to be including a fungicide specific for downy mildew in their spray rotation such as Previcur Flex, Ranman, Presidio, or Tanos at this time. Follow the label directions for plant-back restrictions, mixing partners, such as Bravo and mancozeb, and adjuvants. See the 2009 Commercial Vegetable Productions Recommendations for more information. Check the Cucurbit Downy Mildew ipmPIPE web site as well for more information.

cucurbit downy mildew symptoms on watermeloncucurbit downy mildew symptoms on watermelon

Downy mildew on the upper surface of watermelon leaves. Fungal growth on the underside of the leaves is often sparse.