Late Blight Tomato Spray

Mancozeb

• Mancozeb is a protectant fungicide, so you must apply mancozeb to your plants before infection occurs. Mancozeb carries a warning label of "Caution," meaning that the chemical poses the lowest level of risk. Mancozeb may cause respiratory irritation if inhaled, or skin and eye irritation. Macozeb may break down over time into a chemical with the potential to cause goiter, cancer and birth defects, so follow the label instructions carefully with respect to preharvest applications, as this breakdown can occur on stored tomatoes or during cooking. The fungicide may pose a risk to some wildlife but does not threaten honeybees and doesn't act as a pollutant in the environment.

Chlorothalonil

• Chlorothalonil is another protectant fungicide that will prevent late blight in tomatoes. Warning labels vary, depending on the concentration and formulation of the product, and "Caution," "Warning" and "Danger" labels appear on various chlorothalonil products. Always choose the least toxic product for use in the garden. Because of the high level of variation in chlorothalonil products, toxicity symptoms vary as well. Chlorothalonil has a high potential to cause eye and skin irritation. Chronic effects include kidney problems and cancer. Chlorothalonil persists longer in the environment than mancozeb but does not threaten any wildlife except fish.

Fixed Copper

• Fixed copper acts as a protectant fungicide. It is approved with restrictions for use in organic gardening. Copper products carry labels ranging from the low-risk "Caution" to the serious-risk "Danger." Although a natural fungicide and an essential nutrient for plants and animals, excessive levels of copper can produce toxic effects, so use equal care with copper-based fungicides as you use when handling synthetic chemicals. Copper fungicides can build up in the soil over time, threatening the health of soil microorganisms. Bees and fish are also sensitive to copper products.

Using Fungicides

• Because only protectant fungicides are available for use in home gardens, you'll need to apply the fungicide before late blight symptoms appear. Follow the label instructions carefully with respect to the application amount, method, safety precautions and the harvest of sprayed tomatoes. Cultural controls, such as removing volunteer tomato plants and destroying infected plant material, will lower the risk of late blight infection. The University of Maryland Extension recommends protectant fungicide applications only in years where late blight is present in your area and weather conditions favor its spread. Your local extension office can provide you with more information about the necessity of spraying your tomatoes for late blight.