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Fruit and Vegetables |
Thursday May 8 2003.
Horticultural Crops Research Station, Castle Hayne, North Carolina
Registration 3:00-3:30 p.m.; Sponsored Supper (Pig Pickin') 5:30 p.m.
Disease Management and Fungicide Scheduling; Micropropagation and Plant source studies; Strawberry Varieties and Breeding; Methyl Bromide Alternatives; Weed and Mite Management Updates; Eastern North Carolina research results.
Directions:
Horticulture Research Station, Castle Hayne, North Carolina
(http://www.ncagr.com/Research/hcrschmap.htm)
3800 Castle Hayne Road
Castle Hayne, NC 28429-6519
Telephone: (910) 675-2314 / 0242
Wednesday May 14, 2003.
Central Crops Research Station, Clayton, North Carolina
Program commences at 10:00 a.m. Sponsored Lunch 12:00 noon.
Methyl Bromide Alternatives (Iodomethane, Telone) and how to use them; variety updates; mite, disease and weed control updates.
Directions:
Central Crops Research Station, Clayton North Carolina
(http://www.ncagr.com/Research/ccrsmap.htm)
Central Crops Research Station
13223 US 70 West
Clayton, NC 27520-2127
Telephone: (919) 592-7839
Thursday May 15, 2003.
Buncombe County Field Tour
1:00 – 4:00 p.m. Location: David Snelson's Farm - Leicester, North Carolina. Field Day will be highlighting production practices, pest identification, and management options for strawberries. History of site: 2nd year of MB Alternative Research, 7 alternatives looked at this year including compost. Audience: Commercial Conventional and Organic growers. Contact Diane Ducharme for directions. Email: Diane_Ducharme@ncsu.edu. Telephone: (828) 255-5522.
For more information on the North Carolina strawberry field days, contact the North Carolina State University Department of Plant Pathology by telephone at 919-515-2730 or visit the Small Fruit Center web site at: http://www.smallfruits.org/.
During the last two weeks, we have received a large number of samples in the Plant Disease and Insect Clinic at North Carolina State University and have observed numerous field problems. In general most strawberry fields seem to be performing well despite the amount of rain and temperatures that have been favorable for disease development. Regretfully some fields and some of our research plots are experiencing a very high level of disease. For example, some growers have reported the need to discard 75 percent of their fruit due to anthracnose, particularly in fields where it has been too wet to apply fungicides. In other cases, in fields with a known high risk of potential problems, the levels anthracnose have been low, and this may be due to the effective fungicide programs implemented.
We have observed a rather high level of Phytophthora crown and root rot in several plantings. As the fruit load develops and as the disease progresses in the crown or in the roots, the plant collapses suddenly. In fields where this is a problem, it is possible to apply Ridomil Gold during the harvest season. Growers ask about the use of Ridomil Gold during harvest and the waiting period required after treatment. The label offers no clear guidelines and I pursued this with the company. There is no waiting period for Ridomil when applied through the soil as recommended. This may seem concerning since Ridomil Gold is a systemic fungicide and may pose a health concern. However, the answer probably relates to the anatomy of the strawberry leaves and fruit. Ridomil Gold probably does not accumulate in the fruit, reducing residue concerns. Therefore, in fields where harvest has not reached a peak and plant vigor is good, benefit may be achieved with a Ridomil Gold application if Phytophthora has been diagnosed. The season may be short and the economic benefit of such an application will need to be determined on a field by field basis. Alternatively, if roots are badly damaged, plants have responded well to an Aliette application. These products are not needed if Phytophthora is not present.
Anthracnose problems have been prevalent. There are several problems we have observed. First, many fields have inconsistent plant growth. In our research plots, plants inoculated with the pathogen were stunted all year long compared to non-inoculated plants. Even fall fungicide sprays did not help plants pull out of this stunting problem. Second, many plants have begun to collapse. The pathogen is Colletotrichum acutatum (not considered a crown pathogen) but it appears to have grown in from the top killing the upper portion of the crown. Finally, considerable fruit rot occurred on green fruit early in the season and now on ripe fruit. In plots not sprayed, up to 22 percent of the fruit has anthracnose. Plots sprayed with captan, Cabrio, Quadris or various combinations have an incidence of 3.8 to 8.6 percent (our plots always have a higher level than growers experience due to so much inoculum present in adjacent non-sprayed plots). Regretfully, this disease is active all season if wet warm weather persists. Therefore growers will need to maintain a fungicide program.
There is some confusion about the use of Cabrio and Quadris. Quadris and Cabrio should be considered the same product. They are both stobilurin products with the same mode of action. The difference in the labels leads to confusion. Technically, the most liberal label could be followed; e.g., up to 6 applications of a strobiluron per season (the Cabrio label allows for 6; Quadris allows for only 4). However, there would be a high level of selection pressure for resistant populations of the Colletotrichum pathogen if up to 10 applications per season are applied. Thus, a combined view needs to be taken. Perhaps a generic way to write this is Do not use a strobilurin (Quadris or Cabrio) more than two times in a row and do not use a storbilurin more than 6 times per season, with a limit of 4 applications of Quadris. Thus, in the non-stobilurin weeks and in fields with anthracnose pressure, it is good to apply captan-based products so that there is continuous coverage of a product that has anthracnose activity. The inclusion of a botryticide continues to be important (e.g. Elevate or Switch).
Several growers with high disease levels have questioned the future potential of the crop. Is it worthwhile to continue to spray and hope for a marketable crop? Naturally this is a difficult decision to make. Field observations suggest anthracnose levels will decline after two applications of Quadris or Cabrio. With the use of fungicides and if dry weather occurs, the disease levels should decrease substantially and a marketable fruit can still be obtained, hopefully at economically useful levels.
Botrytis (gray mold) pressure has also been high this spring. However, in field observations and in our fungicide plots, we have been pleased by the relatively low incidence where effective fungicides have been used. If the weather changes and as the season approaches the end, the need for a botryticide fungicide decreases substantially. An Integrated Pest Management (IPM) approach may be to eliminate the use of such fungicides about 24 days before the last expected harvest.
Figure 1: Sudden plant collapse due to anthracnose in the crown. (Photograph by Jim Driver, April 24, 2003)
Figure 2: fruit with anthracnose (top 4) and Botrytis (bottom 2). Weather has favored both problems. (Photograph by Jim Driver, April 24, 2003)
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 5, 2003 by Stephen J. Toth, Jr.
