Posts Tagged ‘bacterial fruit blotch’

Inspect Watermelon and Cantaloupe Transplants, New Bacterial Fruit Blotch Factsheet

Thursday, May 3rd, 2012

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

As watermelon and cantaloupe transplanting continues on Delmarva, growers are reminded to inspect plants before they are transplanted into the field for signs of disease including Bacterial Fruit Blotch, Gummy Stem Blight, and Angular Leaf Spot.

Kate Everts and Gordon Johnson have put together a new factsheet on Bacterial Fruit Blotch, which will be of interest to watermelon growers. It is available online here: http://agdev.anr.udel.edu/weeklycropupdate/wp-content/uploads/2012/05/BacterialFruitBlotchFactsheet.pdf

Preventing Spread of Bacterial Fruit Blotch in Watermelon Transplants

Thursday, April 12th, 2012

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

Now that transplant production is in full swing, it is timely to review what we do and don’t know, about bacterial fruit blotch (BFB) of watermelon. BFB of watermelon is caused by the bacterium Acidovorax avenae subsp. citrulli. Warm, humid conditions in greenhouse transplant houses are highly favorable for the spread of disease and the development of BFB symptoms. Although the disease spreads quickly in the transplant houses, it often is not noticeable in the field until shortly before harvest. There, BFB is damaging because it causes 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. In the image below, the leaves were incubated and the lesions have progressed along the veins and are obvious. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die. The pathogen also causes disease on muskmelon or cantaloupe, honeydew, and on squash and pumpkin.

There are many steps that can lower the risk of development and spread of BFB on watermelon in the transplant house. All seed in a commercial greenhouse should have been tested and found to have “no evidence” of the pathogen. Don’t grow experimental lots that were not tested in a commercial house. Remember too, that testing, and “no evidence” does not guarantee that BFB will not develop, it is one of many steps to reduce the risk of disease. Inspect seedlings beginning at cotyledon expansion and at frequent intervals afterward. If BFB is suspected, send plants to the University of Maryland or University of Delaware diagnostic lab, or the Lower Eastern Shore Research and Education Center, for identification. Destroy all trays with symptomatic plants and those within a five foot radius. Remove adjoining trays to a separate – isolated – area for observation. Monitor these isolated seedlings daily and destroy trays where symptoms develop. All plants in the greenhouse should be sprayed with copper such as Kocide or Nordox. The applications should continue until the plants are shipped or transplanted to the field.

All the greenhouse surfaces should be sterilized prior to the production cycle. A solution of one part of bleach to nine parts of water, or Greenshield or Physan can be used on implements or benches. Don’t reuse trays.

Additional good practices for greenhouse transplant producers are:
· Workers should wash their hands and use a shoe bath when entering the greenhouse to work.
· Minimize the number of people that enter the greenhouse.
· Eliminate all weeds in and around the house.
· Maintain low humidity in the greenhouse.
· Water plants at their base and avoid splash between plants.
· Keep greenhouse flaps closed if it is windy.
· Segregate seedlots and separate them from each other with a vertical plastic sheet to avoid spread by splash or in aerosols.

Bacterial fruit blotch symptoms after incubation. Note the range of symptoms from small lesions on the true leaves to advanced lesions on the cotyledons.

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.

Bacterial Fruit Blotch Detected in GA Watermelon Seedlings

Friday, April 29th, 2011

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

I just received word from Dr. David Langston in Georgia that bacterial fruit blotch (BFB) was confirmed on seedlings destined for shipment to other watermelon producing areas. Some plants may have been shipped before the outbreak was identified. At this time we do not know if any seedlings were shipped to Maryland or Delaware. However, increased scouting of transplants is warranted. Because BFB is seed-transmitted, locally grown transplants should also be examined.

BFB of watermelon is caused by the bacterium Acidovorax avenae subsp. citrulli. The disease is damaging because it causes large olive green to brown water-soaked lesions on fruit (Figure 1), making them unmarketable. Symptoms of BFB on seedlings are water-soaked areas of the lower surface of the cotyledons and inconspicuous lesions on leaves (Figure 2). BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die.

Conditions in greenhouse transplant houses are highly favorable for the development of BFB symptoms and the spread of disease. If BFB is suspected, please send plants to a diagnostic lab (University of Maryland or University of Delaware) for identification. In the meantime, 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. After symptomatic plants and adjoining trays are discarded, spray the remaining trays with a labeled fungicide and continue applications until the plants are shipped or transplanted to the field.

Figure 1. Olive green water-soaked lesion on watermelon fruit. (Image courtesy David B. Langston, University of Georgia, Bugwood.org)

Figure 2. An inconspicuous lesion of bacterial fruit blotch on a watermelon transplant.

 

Watermelon Seedling Diseases in the Greenhouse

Thursday, April 3rd, 2008

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

 The fungal diseases gummy stem blight, Alternaria leaf blight, and anthracnose can be introduced into the greenhouse on watermelon seed or through inoculum from a previous crop. To minimize the occurrence of these diseases, the greenhouse should be disinfected before planting (benches, walls, walkways, etc.). The seed source should have tested negative for the pathogen with a minimum assay number of 1,000 seeds. Use clean transplant trays (disinfect trays if they will be reused) and new soil. 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. Keep relative humidity as low as possible through proper watering and good air circulation in the greenhouse.

 As the seedlings develop, inspect them carefully. Infected seedlings will have small brown lesions on the leaves and/or water-soaked lesions on the stem. 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

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

If the seedlings appear diseased, destroy all trays with symptomatic plants. Remove adjoining trays to a separate area for observation. Monitor these seedlings daily and destroy trays where symptoms develop. Do not ship any trays containing plants with disease symptoms. After symptomatic and adjoining trays are discarded, spray the remaining trays with a labeled fungicide and continue applications until plants are shipped.

 Bacterial fruit blotch (BFB) of watermelon is caused by a bacterium that also is seedborne. Initial symptoms of BFB are water-soaked areas on the lower surface of the cotyledons. BFB lesions will become necrotic often with yellow halos. Lesions are frequently delimited by veins. Infected seedlings collapse and die. Angular leaf spot, which also is a bacterial disease, occurred in Delmarva’s greenhouses several years ago. Symptoms are small, dark brown, irregular lesions on cotyledons or leaves. ALB is favored by cool wet weather. Usually conditions after transplanting to the field do not favor ALB disease development.

bacterial fruit blotch

Small inconspicuous lesion of bacterial fruit blotch

Fusarium wilt also can be seedborne. 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). No lesions are observed along the stem or petiole but the vascular system is discolored and tan, pink or brown. This disease is of special concern because new strains or races can be introduced into an area on seedlings grown from infested seed.