June 2001 Newsletter

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WSU Vegetable Pathology Team Newsletter

Welcome to the June 2001 edition of Washington State University’s Vegetable Pathology Extension Team. This newsletter follows the team’s June conference call when team members discussed current vegetable diseases, diagnoses and control. Please use this information in your own program newsletters and activities.

Update about Vegetable Pathology Team Website

Please view our new website! Considerable work has gone into its design and development, and it is expanding continuously. The new crop rotation publication is now posted.

We would appreciate receiving comments about the site: contact dainglis@wsu.edu

For additions/deletions to the vegetable events calendar: contact gunde@wsu.edu

Another Useful Vegetable Disease Team Website

Michigan State University’s Vegetable Advisory Team newsletters, they present information for muck and upland vegetable pest management including potato production, soil nutrition, and potato late blight management.

Need to Know Current Status of Pathogens & Pests on Washington Vegetables?

Review the crop profiles now being assembled by WSU’s Pesticide Information Center. Each crop profile in this growing collection tells how a commodity is produced, with emphasis on critical pest management needs — including the role of pesticides in integrated pest managament (IPM) and resistance management programs. The development of crop profiles is coordinated in each state by the land-grant university liaison to the regional Pest Management Centers. Their development involves extensive collaboration among land-grant faculty and growers.

• The carrot profile
• The lettuce profile
• The pea (dry) profile
• The sugar beet profile
• The cabbage seed profile
• The spinach seed  profile
• The table beet seed  profile

Vegetable Diseases/Issues and Places to Find Information

Questions to ask and steps to follow when diagnosing vegetable diseases.

1. Identify the symptoms. Are leaves yellow or brown? Is the discoloration worse on the leaf edges or in the middle of the leaf? Are there lesions or cankers on leaves, stems or roots? Are the spots of uniform size, or are they of many different shapes and sizes? Is only the upper or lower surface of leaves showing symptoms? Are plants wilting? Note: Spots uniform in size and distribution may indicate some type of chemical injury. Discoloration on leaf edges might indicate fertilizer toxicity. Mottling and mosaic patterns may indicate a virus infection. Lesions and cankers are generally caused by bacteria or fungi.
2. Determine if there is a pattern to the symptoms. Are many plant species in the same area affected? Does the problem seem worse on the field’s edge or are symptoms uniform throughout the field? Are all plants in a particular row or field affected? Are all of the leaves or shoots on the plant affected? Are affected plants in a low spot or where there is poor drainage or compacted soil? Note: Damage caused by pathogens or insects often shows up as scattered areas on plants or in fields and is usually crop specific. Damage that has a uniform pattern or appears suddenly may be caused by physical, chemical, mechanical or environmental factors.
3. Trace the problem’s history. When were the symptoms first noticed? What rates and types of fertilizer were used? What were the weather conditions like before the problem was noticed? Has the field recently been treated with herbicide? How much mulch has recently been applied?
4. Examine the plants carefully. Look for the presence or signs of insects feeding on leaves, stems and roots. Sometimes it’s easier to find insects early in the morning or toward evening. Pull up plant and examine roots for signs of feeding. If you find an insect, it doesn’t necessarily mean it caused the problem–you still need to get the insect identified. For diseases, look for yellow, discolored, or dead areas on roots, leaves, stems and flowers. The signs of a plant pathogen (fruiting bodies, slime, cysts, etc) might be present. Are the plants stunted or wilted even though there is available soil moisture? This could be from a root rot, wilt disease, or salt injury. Are the plants stunted or do they have obvious growth malformations; are they discolored or mottled? This might be due to infection by a virus.
5. Could plants be lacking essential nutrients? See table below.
6. Could there be a nutrient toxicity? Soluble salt injury may be seen as wilting of the plant even when the soil is wet. Leaf margins may appear scorched or browned, usually resulting from excessive fertilizer application. Burning on leaf edges can be a sign of chlorine damage. Also, if wood ashes were applied to the field, using more than 5 pounds per 100 square feet could increase the soil pH and cause nutritional deficiencies and/or toxicities.
7. Could the problem be related to the soil? Soil problems such as compaction and poor drainage can severely stunt plants and make them susceptible to seedling damping-off and root diseases.
8. Could a pesticide injury be the cause? What pesticides were applied and when were they applied? Copper and sulfur fungicides sometimes can burn plants when applied in hot weather. Also, broadleaf herbicides can cause abnormal growth or kill some plants. Be aware of mulches that may have residual herbicide. Obtain information about the field’s history i.e., crops planted and herbicides applied in prior years.
9. Could the damage be caused by environmental conditions? Have temperatures been excessively high or low? Plants that die practically overnight may have been affected by frost. Has it been very dry or wet for extended periods? Have there been strong winds? What about air pollution? Ozone levels may rise as hot, humid weather settles in for long periods of time, and flecking from damage may be concentrated in specific areas of leaves. Look for irregularly shaped spots that may look similar to feeding damage of mites and certain leafhoppers.

Some Nutrient Deficiency Symptoms

Nitrogen	light green or yellow older foliage
Phosphorus	stunted plants and purplish leaves
Calcium	stunted plants, stubby roots, causes blossom end rot of tomatoes, tip burn of cabbage, brown heart of escarole, celery blackheart, carrot cavity spot
Magnesium	yellowing between veins of older leaves
Sulfur	yellowing of new leaves, stunted plants
Boron	growing points die back and leaves are distorted
Copper	yellowing of leaves which become thin and elongated; soft onion bulbs with thin scales
Iron	light green or yellow foliage on youngest leaves
Zinc	rust colored spots on seed leaves of beans, green and yellow striping of corn, yellowing of beet leaves
Manganese	mottled yellow areas appearing on younger leaves first. In beets, foliage becomes dark red
Molybdenum	distorted, narrow leaves, yellowing of older leaves, whiptail leaf symptoms in cauliflower

-Adapted from American Vegetable Grower, February 1998

10. Seek the advice of a professional. If you need assistance with plant disease diagnoses, you can submit a sample to the WSU plant clinics.

Is this mildew downy or powdery?

Downy mildew and powdery mildew are two foliar diseases which are sometimes confused with one another, but actually are distinct and relatively easy to tell apart. The pathogens causing both types of mildew are obligate parasites, and require an association with host tissue for long term survival. However, the downy and powdery mildew organisms belong to different groups of plant pathogens. This means that different types of fungicides are required in their control – an important fact often overlooked. Both mildews occur in Washington although downy mildew is more common in the western part of the state while powdery mildew generally is more common on vegetables in eastern Washington. The following comparisons might be useful for distinguishing between the two diseases since only a few crops (beet and green pea) can be affected by both.

Register Now for the Second International Vegetable Soybean Conference

The conference will be held August 10-12 at the Sheraton Tacoma Hotel.
E-mail: wsuconf@wsu.edu or milesc@wsu.edu for more information.

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