Stephen J. Toth, Jr., editor
Volume 19, Number 5, May 14, 2004

Fruit and Vegetables

From: Gerald J. Holmes, Extension Plant Pathologist, and Zvezdana Pesic-VanEsbroeck, Director, Micropropagation Unit

White rust is a common occurrence on sweetpotato leaves during warm and wet conditions in late summer. The disease has not been considered an economic threat because it does little damage to the foliage. This year, for the first time, we saw white rust on sweetpotato transplants produced in the greenhouse. This is not surprising since the greenhouse is an excellent environment for this disease (i.e., high humidity and high temperature) and the causal agent (Albugo ipomoeae-panduratae) attacks many wild and cultivated relatives of the sweetpotato (i.e., members of the family Convolvulaceae) that are widespread throughout the state.

As in the field, it appears that white rust causes little damage to sweetpotato plants in the greenhouse. In this particular outbreak, the disease was confined to the oldest leaves deep within the canopy of densely-grown plants. Most plants had some level of disease on them. Angular chlorotic patches occur on the upper leaf surface while sporulation of the fungus generally occurs on the lower leaf surface in the form of small, white pustules.

Although we do not believe that the occurrence of white rust in greenhouses is cause for alarm, we are interested in how this will play out in the field. It may be that with dry weather in the spring, the disease will subside. On the other hand, it may subsist through the spring and appear earlier than ever when wet, warm weather persists. It is still an open question as to whether it would ever pose an economic threat to the crop. In any case, starting the season with diseased plant material is not desirable.

Growers should consider the following guidelines for managing white rust in the greenhouse:

1. Avoid long periods of very high humidity.

2. Reduce humidity in the plant canopy by increasing plant spacing and air movement.

3. Avoid practices that will spread inoculum throughout the greenhouse (e.g., mowing and overhead irrigation).

4. Control morning glory and other wild and cultivated species of Ipomoeae in the vicinity of the greenhouse.

5. Practice strict sanitation of the greenhouse environment including complete removal of plant material and sanitation of greenhouse surfaces between growing seasons.

6. Two products are labeled for use on sweetpotatoes that would have activity on white rust -- Ridomil Gold EC and Quadris. Ridomil Gold is labeled as a preplant incorporated application at 1 to 2 pints per treated acre or as a surface application at planting (same rate). Quadris can be applied at 6.2 to 15.4 fluid ounces per acre. At this time we do not have direct experience with the efficacy of these products.

From: Ken Ahlstrom, Agricultural Research Specialist, Plant Industry Division, North Carolina Department of Agriculture and Consumer Service

Giant African Land Snails are being used increasingly in science lessons in schools. These snails are illegal in the continental United States because they are highly invasive, and can cause extensive damage to important food crops and other agricultural and natural resources. These snails can also pose a risk to human health (for information, see http://www.cdc.gov, or call your state health department). The U. S. Department of Agriculture's Animal and Plant Health Inspection Service is interested in finding these snails, and encourages those using these snails in classrooms, nature facilities, or keeping them as pets to turn them in voluntarily without fear of penalty.

If you receive or find a Giant African Land Snail, PLEASE DO NOT RELEASE IT INTO THE ENVIRONMENT OR GIVE IT AWAY. Instead, report it to the U. S. Department of Agriculture, Animal and Plant Health Inspection Service in Wilmington, Raleigh, Charlotte, and Goldsboro. If you are unable to find the local number, please call 919-855-7600 or visit the following web site: http://www.ceris.purdue.edu/napis/names/sphdXstate.html). For further information contact the North Carolina Department of Agriculture and Consumer Services, Plant Industry Division at 919-733-6930 or toll-free at 1-800-206-9333. You may also visit our web site at http://www.ncagr.com/plantind/. Arrangements will be made for an official to pick up the snails.

Giant African Land Snail is the common name used to describe any of three snail species native to Africa and considered serious agricultural pests in the United States. The giant African snail (Achatina fulica), the giant Ghana tiger snail (Achatina achatina), and margies (Archachatina marginata) are large, terrestrial snails that reach up to 20 cm (8 inches) in length and 10 cm (4 inches) in maximum diameter. These snails are about the size of an average-size adult fist. The brownish shell with darker brown vertical stripes covers at least half the length of the snail.

Giant African snails have a voracious appetite. They are known to eat at least 500 different types of plants, including peanut, beans, peas, cucumbers, and melons. If fruits or vegetables are not available, the snails will eat a wide variety of ornamental plants, tree bark, and even paint and stucco on houses.

These snails also reproduce rapidly, laying as many as 100 to 400 eggs in a single session. Snails contain both male and female reproductive organs, and can lay up to 1,200 eggs per year.

At the present time snails found in the United States have not been shown to be disease carriers. For more information, see the following web site: http://www.cdc.gov/ncidod/dpd/parasites/angiostrongylus/factsht_angiostrongylus.htm.

Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Last modified on May 17, 2004 by Stephen J. Toth, Jr.