By Fran Pontash (June 2017)
There is no argument that winemakers prefer quality fruit that is free of disease and insect injury. Quality fruit is an indication of healthy vines and good viticulture management. Healthy vines are capable of producing higher yields with relative consistency, and the vines tend to live longer. This potential for higher return on investment has a solid disease and insect management program serving as its backbone.
Quite frequently we are asked, “Do you have a schedule I can follow so I know when and what to spray?” What we have is more than that. The annually published guide, Texas Grape Pest Management Guide describes fungicide and insecticide applications, the growth stage when certain spray applications are most needed, chemical options, modes of action, efficacy, symptom identification, and more. However, it is up to each grower to determine the ultimate timing and choice of chemical(s) with which to spray his/her vines.
Why can’t we offer a one size fits all prescribed schedule? In order to control diseases and pests, a prescribed schedule would demand one to spray so frequently that he rids the site of all flying, crawling, sporulating, and replicating organisms. This type of spray plan deploys excessive and expensive amounts of chemicals, and is a potential environmental debacle, posing a hazard to humans, animals, aquatic life, and neighborly relations. A clearer understanding of what, when, and why to spray can avoid a cycle of over application.
Integrated Pest Management (IPM). “IPM is an effective and environmentally sensitive approach to pest management that relies on a combination of common-sense practices”. Vineyard practices that alter the environment such as opening the canopy to optimize air movement and sun penetration, frequent mowing and managing irrigation help reduce the number of chemical pesticide applications that are necessary. An IPM strategic plan improves chemical efficacy, whether organic or conventional improving fruit and vine health. It hinges on prevention and since some of the diseases that we wrestle with have no cure, prevention literally pays off by saving vines and crops.
Prevention. Prevention relies on obtaining knowledge of our grapevines, their environment, diseases, insects, and the chemicals we use. This begins with selecting suitable plant material. Grape varieties and rootstocks differ in their ability to tolerate certain diseases, weather conditions, and soil character. There is information available on specific rootstock and variety characteristics, so don’t hesitate to consult with your viticulture program specialist.
In addition, consider that some varieties are more susceptible to certain diseases, insects and animals than others. Some examples are Desmia funeralis, the grape leaf-folder that feeds on Lenoir, powdery mildew on Tempranillo, and deer feeding on Blanc Du Bois.
Sanitation. A clean vineyard can prevent outbreaks. An open, trained canopy maximizes air flow and spray penetration. Wood, leaf, and cluster debris removed from the vineyard floor helps to prevent disease by removing insect eggs, larvae and fungal pathogens on dead and dying plant tissue. Frequent mowing prevents weeds from forming mature seed heads. Uncontrolled weed growth competes with vines for nutrients and water, and weeds typically win leaving vines weakened and vulnerable to drought, nutritional disorders, and insect infestation.
Frequency. Spray applications begin during dormancy and continue until senescence. Pesticides have become more efficient and specific in their mode of action; it is important to rotate chemical applications by their mode of action. Pesticides can be overused to the point that the target pathogens or insects develop a resistance to their particular mode of action. Rotating chemicals with different modes of action helps to avoid overusing some of our most effective chemicals.
Maintaining a healthy canopy begins with dormant sprays and sprays continue until senescence. Pesticides use different modes of action that are often target specific. It is important to rotate applications by mode of action. Using chemicals with multiple modes of action helps reduce the ability of target pathogens, insects, and weeds to develop a resistance to the active ingredients of the pesticide. Read all pesticide labels for target pest, appropriate application and resistance management. Don’t hesitate to consult your viticulture program specialist if you have questions.
Note: Fungicide Groups 3, 7, and 11, signifying modes of action, are repeated and circled in red.
Always read and follow the directions on the label, and calibrate the output of your sprayer to know its rate of application. Use a separate sprayer for herbicides. Some combinations of insecticides, fungicides, and fertilizers can be harmful if tank mixed while others mix easily in a spray application. Before mixing, test the chemical compatibility of what you want to spray. In a jar half filled with water, add the proportionate amounts of each chemical. Shake for 15 minutes. The formation of heat, scum, clumps, and a high degree of solid precipitates indicate chemical incompatibility and should not be applied. Read the following caution found on Rampart’s label:
“COMPATIBILITY Mixing Rampart Fungicide with certain surfactants, foliar fertilizers or other pesticides may cause crop injury. Rampart Fungicide is a slightly acidic buffer solution. Avoid mixing Rampart Fungicide with strongly acidic or alkaline materials. Do not tank mix without first testing the mixture’s compatibility nor apply it without assessing its safety to the crop (phytotoxicity).” (2017. Loveland Products. Rampart Fungicide. p. 3).
Timing. Temperature, rainfall and humidity determine disease and insect emergence, thus they determine the timing and choice of sprays that are most effective. Optimizing the timing increases the efficacy of each application and the cost of each chemical purchase. It requires an understanding of the differences between the diseases, insects, and weeds, their times of emergence, their strengths and weaknesses, and the symptoms and signs that they leave behind. Gaining a better understanding of pests and pesticides is an ongoing process. Good record keeping helps immensely. A custom program can be created from recordings of previous weather conditions, chemicals used, timing, and observations of symptoms. Updating our knowledge base has becomes increasingly important as new technology, urban encroachment, and the discovery of previously unrecognized diseases continue to unfold.
Insecticide applications can be optimized by monitoring the emergence of populations so that the highest number of insects are controlled per spray. Sticky traps for sharpshooters and pheromone traps for grape berry moth help monitor the time and severity of their emergence.
General. Most newly planted vineyards experience a grace period in regards to grape fungal diseases. The diseases eventually infect your vineyard, overwinter in it, and take advantage of tender new growth each spring. Insect pests such as grasshoppers and vectors of Pierce’s Disease prefer tender growth and feed on new tissue especially in areas of high risk to insect pressure.
The Grape Pest Management Guide outlines disease and insect pressure by vine growth stage. The outline includes lists of our most frequently used chemicals. Efficacy and modes of action are also included. Don’t hesitate to contact a program specialist with your specific questions.