Posts Tagged ‘watermelon anthracnose’

MELCAST Fungicide Scheduling for Watermelon

Friday, May 18th, 2012

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

Gummy stem blight (caused by Didymella bryoniae) is the most important foliar disease of watermelon in Maryland and Delaware. The disease affects leaves (Fig. 1), stems and vines of watermelon, resulting in fewer and smaller fruit. Anthracnose (Fig. 2), which is caused by Colletotrichum orbiculare, also occurs yearly. In MD and DE, yield losses due to gummy stem blight and anthracnose of 20 to 100% would occur in the absence of effective fungicidal control.

Beginning in 1997 the DE IPM, MAR-DEL Watermelon growers, Maryland Vegetable growers, and other grant funds have supported dissemination of a weather-based fungicide application program for watermelons, Melcast. Melcast is a weather-based spray advisory program for watermelon developed at Purdue University. The program uses hours of leaf wetness and temperature during leaf wetness periods to determine when a fungicide should be applied. In MD and DE, we have slightly modified Melcast so that fungicides are scheduled earlier. As a result, fungicides scheduled by Melcast, successfully manage anthracnose and gummy stem blight. Growers that use Melcast report reducing their fungicide applications by two per season compared to standard schedules. Six research trials were conducted over three years in our region to evaluate Melcast. In four of those trials yield was the same when sprays were applied according to Melcast compared to weekly applications. In one trial yield was higher, and in one trial yield was lower, when sprayed according to Melcast in comparison to weekly sprays.

Since our original trials of Melcast, several newer and highly effective fungicides have been registered for gummy stem blight and anthracnose. We are testing Melcast again with these effective materials. To use Melcast on your farm, please call Karen Adams at (302)856-7303 and give us your name and Fax number or e-mail address. More details about how the program works are available at our Disease Forecasting Web page: http://mdvegdisease.umd.edu/forecasting/index.cfm

Figure 1. Large dark brown foliar lesions of gummy stem blight

Figure 2. Anthracnose lesions on cucurbits are angular in appearance. Tiny black spots can be seen through a hand lens in the tan centers of lesions.

MELCAST for Watermelons

Friday, May 11th, 2012

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

The weather based forecasting program MELCAST on watermelon will begin next week. MELCAST is a weather-based spray scheduling program for anthracnose and gummy stem blight of watermelon. If you received a report in 2011, you should automatically receive the first report next week. If your email or fax number has changed, please call us. If you do not receive a report and would like to, please call Karen Adams at (302)856-7303 and give us your name and Fax number or e-mail address. MELCAST also is available online – bookmark the site http://mdvegdisease.umd.edu/forecasting/index.cfm. Click on the watermelon picture.

To use MELCAST for watermelons, apply the first fungicide spray when the watermelon vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 30 EFI values have accumulated by the weather station nearest your fields. Add 2 points for each overhead irrigation that is applied. After a fungicide is applied, reset your counter to 0 and start over. If a spray has not been applied in 14 days, apply a fungicide, reset the counter to 0 and start over. Please call if you have any questions on how to use MELCAST on your crop (Kate Everts at 410-742-8789).

Do not use Quadris, Cabrio or Flint on watermelons in Maryland or Delaware. Under low disease pressure, use Chlorothalonil (Bravo, etc.) applied according to MELCAST. Under high disease pressure alternate chlorothalonil with Pristine plus chlorothalonil, Folicur plus chlorothalonil, Inspire Super plus chlorothalonil or Luna Experience plus chlorothalonil applied according to MELCAST. If a severe disease outbreak occurs in your field, return to a weekly spray schedule.

Watermelon Seedling Diseases in the Greenhouse

Thursday, April 5th, 2012

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

Bacterial fruit blotch (BFB)
BFB
of watermelon, which is caused by the bacterium Acidovorax avenae subsp. citrulli, produces large olive green to brown water-soaked lesions on fruit, making them unmarketable. Symptoms of BFB on seedlings are water-soaked areas of the lower surface of the cotyledons and inconspicuous lesions on leaves. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die.

If the bacterium is present, conditions in greenhouse transplant houses are highly favorable for the development of BFB symptoms and the spread of disease. Good practices for greenhouse transplant production are to disinfect surfaces before planting (benches, walls, walkways, etc.). The seed source should have tested negative for the pathogen with a minimum assay number of 10,000 seeds. Clean transplant trays (disinfect trays if they will be reused) and new soil must be used. Destroy any volunteer seedlings and keep the area in and around the greenhouse weed free. Avoid overhead watering if at all possible, or water in the middle of the day so that the plants dry thoroughly before evening. The bacterium can spread on mist and aerosols, so keep relative humidity as low as possible through proper watering and good air circulation in the greenhouse. Separate different seedlots, to reduce lot-to-lot spread. If BFB is suspected, collect a sample and submit it to your Extension educator, or specialist. Destroy all trays with symptomatic plants. Remove adjoining trays to a separate – isolated – area for observation. Monitor these isolated seedlings daily and destroy trays where symptoms develop. The remaining trays should be sprayed with a labeled fungicide and the applications continued until the plants are transplanted to the field.

Olive green water-soaked lesion on watermelon fruit. (Image courtesy David B. Langston, University of Georgia, Bugwood.org)

An inconspicuous lesion of bacterial fruit blotch on a watermelon transplant.

Other Greenhouse Diseases:

Angular leaf spot, which also is a bacterial disease, looks similar to BFB. This “look-alike” disease occurred in Delmarva’s greenhouses several years ago. Symptoms are small dark brown irregular lesions on cotyledons or leaves. Angular leaf spot is favored by cool wet weather. Usually conditions after transplanting to the field do not favor angular leaf spot disease development.

The fungal diseases gummy stem blight, Alternaria leaf blight, anthracnose, and Fusarium wilt can also be introduced into the greenhouse on watermelon seed or through inoculum from a previous crop. Diseases that are transmitted on seed often are randomly located throughout the greenhouse. Initial infections will occur as ‘foci’ or clusters of diseased plants.

Gummy stem blight infected transplants occur as clusters in an area around the initial infected seedling (foci).

Although I have not seen Fusarium wilt infected transplants in local commercial greenhouses, it has occurred in other states. Symptoms are wilted seedlings that may remain green or become chlorotic (yellow). This disease is of special concern because new strains or races can be introduced into an area on seedlings grown from infested seed.

Bottom line: If the seedlings appear diseased, identification of the problem is critical. Do not ship any trays containing plants with disease symptoms.

MELCAST for Watermelon

Friday, May 27th, 2011

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

The weather based forecasting program MELCAST on watermelon began on Wednesday (May 25). MELCAST is a weather-based spray scheduling program for anthracnose and gummy stem blight of watermelon. If you received a report in 2010, you should have automatically received the first report. If your email or Fax number has changed, please call us. If you did not receive a report and would like to, please call Jeri Cook at (410) 742-8788 and give us your name and Fax number or e-mail address. MELCAST also is available online – bookmark the site http://mdvegdisease.umd.edu/. Click on the watermelon picture.

To use MELCAST for watermelons, determine which site is closest to your farm field. Apply the first fungicide spray when your watermelon vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 30 EFI values have accumulated by the weather station nearest your fields. Add 2 points for each overhead irrigation that is applied. After a fungicide is applied, reset your counter to 0 and start over. If a spray has not been applied in 14 days, apply a fungicide, reset the counter to 0 and start over. Please call if you have any questions on how to use MELCAST on your watermelon crop (Kate Everts at 410-742-8789).

Because there is widespread resistance to strobiluron (group 11) fungicides in Maryland and Delaware, growers should alternate one of the following with chlorothalonil (Bravo, etc.); a tebuconazole product (such as Folicur), Inspire Super, or Switch. Resistance to Pristine has been recorded in many watermelon fields in the southern U.S. We have not found resistance to Pristine here in Delaware or Maryland, yet. However, Pristine should be used with great caution; always tank mixed with chlorothalonil; and alternated with a fungicide that has a different mode-of-action. If a serious disease outbreak occurs in your field, return to a weekly spray schedule.

 

MELCAST Disease Forecasting for Watermelons

Friday, May 15th, 2009

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

The weather based forecasting program MELCAST on watermelon will begin in the next week. MELCAST is a weather-based spray scheduling program for anthracnose and gummy stem blight of watermelon. If you received a report in 2008, you should automatically receive the first report next week. If your email or fax number has changed, please call us. If you do not receive a report and would like to, please call Jeri Cook at (410) 742-8788 and give us your name and fax number or e-mail address. MELCAST also is available online – bookmark the site http://mdvegdisease.umd.edu/forecasting/index.cfm. Click on the watermelon picture.

To use MELCAST for watermelons, apply the first fungicide spray when the watermelon vines meet within the row. Additional sprays should be applied using MELCAST. Accumulate EFI (environmental favorability index) values beginning the day after your first fungicide spray. Apply a fungicide spray when 30 EFI values have accumulated by the weather station nearest your fields. Add 2 points for each overhead irrigation that is applied. After a fungicide is applied, reset your counter to 0 and start over. If a spray has not been applied in 14 days, apply a fungicide, reset the counter to 0 and start over. Please call Kate Everts if you have any questions on how to use MELCAST on your crop (410) 742-8789.

Because of widespread resistance to Quadris in our area, chlorothalonil (Bravo, etc.) or Pristine plus chlorothalonil alternated with chlorothalonil is recommended when spraying according to MELCAST. If a serious disease outbreak occurs in your field, return to a weekly spray schedule.