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The Grape Grower's Notebook 

 

Grape Grower's Notebook
March 20, 2000

Pesticides for the Organic Grower

In general, this page addresses year two and subsequent years in an organic vineyard . Year one is principally directed to keeping the new plants alive. Fungal pests and insect damage should not be a problem in year one. Deer and rodent damage can be severe.

Insect control is not covered here and is not advocated as a part of the organic vineyard operators routine. Common insect problems are covered in "Grapevine Maladies and Pests."

 Supposedly and to the extent possible, your organic vineyard aspirations have influenced your selection of a site and varieties which will tend to reduce pest problems. Your management practices are designed to help the vineyard be an organic one, and your vigilance is unwavering. At this point, you simply have to prepare yourself for things that may go wrong.

You should read the material provided in the GGN, books and internet resources on Black Rot, Powdery Mildew, Downy Mildew and Botrytis. Hopefully, your reading will be as close as you ever get to these pests. Keep the following thumbnail descriptions in your head.

  • Black Rot attacks clusters and does very little damage to leaves. Its spores probably entered the flowers at bloom. When it becomes evident in clusters, all or part of the crop is going to be lost. Some varieties are resistent to it and some sites do not host it. Where prevention is necessary, early-season pesticide applications and good vineyard sanitation may suffice.
  • Botrytis also attacks grape clusters (especially tight ones) and probably enters the flower cluster at bloom. It sometimes shows up so close to harvest that it may be handled by culling a few berry clusters. Where it gets established early and favorable conditions exist, it can ruin a crop.
  • Powdery Mildew germinates on the top surface of leaves and likes dry, shaded conditions such as tight canopies and fruit zones. When it is seen on exterior foliage, it probably has established itself on hidden parts of the vine. Some varieties are very resistant to it. Preventive sprays and good canopy and fruit zone management should keep it under control.
  • Downy Mildew requires wet conditions and is only a major threat in areas or seasons of abnormal rainfall. It's calling card is a downy patch on the bottom of a leaf. When viewed from the top, the patch looks like an oil spot. If rain persists, Downy will become established and the results (read) are devastating for one season and carry over into the second season. On the other hand, if you are blessed with dry weather, the calling card on the leaf may be all you ever see.

Pesticide Use

The use of pesticides in vineyards may be compared to standing on a ladder. The first rung is "no pesticides for prevention or treatment of maladies." The top rung is "purchase and application of every new promising pesticide that comes onto the market." As mentioned above, you can stay on the first rung until trouble arrives and then decide which rung you want to stand on between these two extremes.

Rung two is sulfur. It is protective and, to a degree, preventative for Powdery Mildew. The presence of sulfur on leaves prevents germination of Powdery Mildew spores. It has no residual effect and must be applied into those dry shaded areas of canopy and fruit zone mentioned above. The use of a surfactant to spread the material evenly over the leaf surface is recommended.

Rung three is Bordeaux Mixture. This preparation of copper sulfate and hydrated lime kills the spores of Powdery, Downy, Black Rot and Botrytis with which contact is made. It is short on control of Black Rot and Botrytis only because spores in grape clusters may have been missed. Bordeaux mixture was discovered by Millardet over 100 years ago. A similar preparation is in use in Burgundy consisting of soda ash instead of hydrated lime. These preparations are especially valuable in areas/seasons of excessive rainfall because they are inexpensive and the contact killer character permits application before and after rain. In these conditions, expensive systemic pesticides would not stand a chance of entering plant tissue and doing their job. Recipes for both preparations may be clicked at the bottom of this page.

Rung four is the use of a proprietary pesticide for Black Rot. We like Mancozeb which was described as an organic pesticide when introduced. Mancozeb (sold under several brand names) is classified as a contact fungicide with preventive activity. "It inhibits enzyme activity in fungi by forming a complex with metal-containing enzymes including those involved in production of adenosine triphosphate (ATP)."(1) Its principal ingredients are manganese 80%, zinc 16%, ethylene bisdithiocarbamate ion 2%. Mancozeb also provides excellent protection against Downy Mildew.

Rung five involves Botrytis protection and calls for an application of benomyl (Benlate ) at bloom for each variety in your vineyard. This is minimal protection for this pest and may well follow the first year you have a Botrytis problem.

Every step on the ladder moves you further away from the organic method. Since that is what prompted you to read this section in the first place, the discussion of other alternatives does not seem appropriate.

There are some promising "home remedies" being bandied about. The use of baking soda, or hydrogen peroxide to control powdery mildew has received recent publicity. This activity is praiseworthy and is how we got Bordeaux Mixture. We say, keep up the good work!

(1) United States Department of Agriculture.
 



 

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