Posts Tagged ‘cucumber’

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.

 

 

Downy Mildew Updates – June 24, 2011

Friday, June 24th, 2011

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

Basil Downy Mildew
Downy mildew on basil has been confirmed in Dunkirk, MD (Calvert County between the DC metro area and Southern Maryland). The infected plants are in a homeowner’s yard, but commercial growers should be on the lookout.

Cucurbit Downy Mildew
As a result of slightly more favorable conditions, Downy mildew on cucurbits is moving northward. Within the last week there have been three reports of downy mildew on CUCUMBER in North Carolina, including one on the border of Virginia. The Cucurbit Downy Mildew forecaster says that disease spread is possible in the mid-Atlantic region, including areas in southern Maryland, the eastern shore, and in Delaware. Scout plants rigorously and monitor the CDM website http://cdm.ipmpipe.org/

Lower leaf surface of a cucumber leaf infected with downy mildew. Courtesy of Gerald Holmes, Valent USA Corporation, Bugwood.org

Downy mildew symptoms on upper leaf surface of cucumber.

Downy mildew symptoms on watermelon, note the differences.

 

Results of the 2010 On-Farm Cucurbit Powdery Mildew Fungicide Resistance Trial

Friday, June 10th, 2011

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

In 2010 a multi-state project including DE, PA, MD, VA, NY and NJ was undertaken to determine the extent of resistance to fungicides for powdery mildew control in cucurbits. Plants of a susceptible pumpkin variety were grown to the 2-3 leaf stage, sprayed with different fungicides at varying rates and placed in commercial cucurbit fields with powdery mildew for 1-2 days. The plants were collected and allowed to continue to grow and develop symptoms in a greenhouse, then evaluated for the amount of powdery mildew on the leaves compared to the untreated plants exposed at the same time. The results from the two fields in DE showed that at least for these two fields that there is resistance in the powdery mildew populations to Topsin M, Flint, Endura, and Rally. The resistance to Rally at the high rate was very low indicating that some control would be expected at the highest label rate of Rally. No resistance was detected to Quintec, either in DE or any other state. I did not include Inspire or Folicur. No resistance was found to Inspire, but NY and PA did see some resistance to tebuconazole (Folicur). Cucurbit growers in DE and MD should not expect to see control of powdery mildew from thiophanate-methyl (TopsinM), or a stand-alone strobilurin fungicide like Flint, Quadris or Cabrio. The results of this trial indicate that the high rate of Pristine (Endura plus Cabrio) may still provide some control but there is resistance to the boscalid (Endura) component occurring in the region.

 

Grafted Vegetables

Thursday, May 12th, 2011

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

Using grafted vegetables for field production is relatively new practice in the United States. However, it is a common practice in Asian countries as well as other areas of the world.

Grafting involves selecting a rootstock that will confer some desired trait, usually resistance to a soil-borne disease. A scion plant is selected, normally the crop and variety with the horticultural traits desired. The scion is grafted onto the rootstock. For example, with tomatoes, a seedling is severed just above the cotyledon. The above-ground portion (scion) of a desired variety for harvest is secured to the root system (rootstock) of the disease-resistant seedling. Once the grafted transplants heal, they can be planted in the field for normal production.

Vegetables that have been successfully grafted include tomatoes, peppers, and eggplants and watermelons, cantaloupes, cucumbers, and other cucurbits.

Grafting can be effective as a non-chemical control method for many soilborne diseases such as Verticillium wilt and Fusarium wilt in tomatoes, Fusarium wilt in watermelons, and root knot nematodes in tomatoes and cucurbits.

Grafting onto vigorous rootstocks can also allow plants to be more stress tolerant because the rootstock has a greater rooting area. This will allow for better water stress and heat tolerance.

Grafting can also improve overall productivity of crops when no disease or stress is present. Again, the vigorous root systems can improve overall nutrient and water uptake and increase fruit yields. In watermelons, rootstocks have been shown to improve fruit quality and holding ability in the field.

Much research is underway on grafted vegetables throughout the region and several growers have started to use grafted plants for production.

 

Cucurbit Downy Mildew Update – July 16, 2010

Friday, July 16th, 2010

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

Wednesday’s rain was a high risk event for cucurbit downy mildew in the region. Be sure downy mildew fungicides are being employed for disease control at this time. There have been no new reports of downy mildew in DE, MD, NJ or PA. That will probably change if this weather pattern continues. Keep current on disease progress by visiting http://cdm.ipmpipe.org/.

Cucurbit Downy Mildew Found in Delaware

Friday, July 9th, 2010

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

Downy mildew was found on July 7 in the sentinel plot near Georgetown on cucumber. Only a few leaves were exhibiting symptoms and less than 5% of the leaf surface was infected. The fungus was not prospering but it was present. This fungus can survive the heat of the last few days and with fog in the early morning the fungus appears to be persisting. Growers should be including downy mildew specific products in their fungicide programs at this time. The risk of spread from southern sources is low at the present time. New reports of downy mildew have been posted from MI, WI, and additional counties in OH and NY. Continue to monitor for downy mildew and check the ipmPIPE website for the latest forecast at http://cdm.ipmpipe.org/.

Vegetable Disease Update – July 2, 2010

Friday, July 2nd, 2010

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

Cucurbit Downy Mildew
We are at minimal risk at the present but keep up to date by checking the ipm PIPE website http://cdm.ipmpipe.org 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; bobmul@udel.edu

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:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
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.)
or
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5 to 18.5 oz 38WG/A
or
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:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
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:
Alternate:
Rally (myclobutanil, 3) at 5.0 oz 40WSP/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0 to 8.0 oz 50WS/A plus chlorothalonil at 2.0 to 3.0 pt 6F/A
or
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
or
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.

Powdery Mildew on Cucurbits

Friday, July 24th, 2009

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

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 PM has been found in the region and/or when 1 lesion is found on the underside of 45 leaves. Fungicide resistance management of the fungus which causes powdery mildew is critical in the Mid-Atlantic region! Fungicides with a high risk for resistance development, such as the strobilurin fungicides (Pristine, FRAC code 11) and Rally or Procure (FRAC code 3), should be tank mixed with a protectant fungicide such as chlorothalonil (M5) and rotated with fungicides of a different chemistry.

The following are some fungicide recommendations for control of powdery mildew in a variety of crops:

To control powdery mildew in pumpkin and winter squash:
Alternate:
Nova or Rally (myclobutanil, 3) at 5.0 oz 40WP/A plus chlorothalonil at 2.0-3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0-8.0 oz 50WS/A plus chlorothalonil at 2.0-3.0 pt 6F/A

With:
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.
or
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5-18.5 oz 38WG/A

If powdery mildew has become well established in the mid to late part of the season, only apply protectant fungicides such as chlorothalonil or sulfur or Quintec* (quinoxyfen, 13) at 6.0 oz 2.08F/A plus chlorothalonil at 2.0-3.0 pt 6F/A.

*Quintec (quinoxyfen, FRAC code 13) from Dow AgroSciences has a section 3 supplemental label for powdery mildew control on pumpkin, winter squash and gourd. The label is available at http://www.rec.udel.edu/update09/Quintec.pdf.

To control powdery mildew in summer squash and cucumbers:
Alternate:
Nova or Rally (myclobutanil, 3) at 5.0 oz 40WP/A plus chlorothalonil at 2.0-3.0 pt 6F/A,
or
Procure (triflumizole, 3) at 4.0-8.0 oz 50WS/A plus chlorothalonil at 2.0-3.0 pt 6F/A

With:
chlorothalonil plus Pristine (pyraclostrobin + boscalid, 11 + 7) at 12.5-18.5 oz 38WG/A

To control powdery mildew in muskmelon and watermelon:
Alternate:
Nova or Rally (myclobutanil, 3) at 5.0 oz 40WP/A plus chlorothalonil at 2.0-3.0 pt 6F/A
or
Procure (triflumizole, 3) at 4.0-8.0 oz 50WS/A plus chlorothalonil at 2.0-3.0 pt 6F/A

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

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