Many different types of pesticides and herbicides cause damage to grapevines. It can be difficult to control damage to grapes due to pesticides, because damage often occurs through the actions of others. In spite of the difficulty to completely control the damage, a proper understanding of the symptoms, causes and impact herbicides have on grapevines leads to a reduction in damage.
Many classes of herbicides damage grapevines. Herbicides that cause the most damage contain a phenoxy-type ingredient. More than 100 different herbicides contain phenoxy. The phenoxy-based herbicides are popular because they are an effective and inexpensive means of controlling weeds such as nightshade, pigweed, morning glory and cocklebur.
The use of phenoxy-based herbicides prevents these pesky weeds from destroying lawns and crops grown for food, and are a popular choice for weed control by professional and home gardeners. The use of phenoxy-based herbicides does not require a license; they are available for purchase at home improvement stores, department stores and garden shops.
Grapevines are particularly sensitive to phenoxy-type herbicides. Sensitivity occurs throughout the growing season, but increases in the early growing season, when the vines blossom and the fruit sets. Flower clusters are more sensitive than other parts of the grapevine. Damage to flowers reduces the amount of fruit produced or delays maturation. Injured grapevines may take one to three years to recover.
Grapevines damage by herbicides often occurs when nearby lawn or crops receive treatment for weeds. Even when a gardener personally avoids the use of herbicides, his crops may still be at risk due to off-target drift. Aerial application of herbicides may affect grapevines as far as 40 miles from the application site. Even slightly windy conditions carry herbicides from the intended crops to grapevines. Temperatures above 70 degrees Fahrenheit cause the herbicides to vaporize; the chemicals then easily carry through the wind for several days, damaging grapevines for miles.
Herbicide damage appears more obvious on young grape plants, including the tips of new shoots and newly formed leaves. Damaged leaves are smaller and narrower in shape, and have veins that lack chlorophyll. Small spots and puckers appear on leaves damaged by herbicides, and damaged clusters of flowers have few or no berries.
Prevention of damage by herbicides requires the cooperation of neighbors. Many neighbors may not understand the damage caused to grapevines by herbicides. Informing neighbors of the risks and providing tips for reducing damage go a long way toward reducing damage to grapevines by herbicides. For instance, advise neighbors to avoid spraying their crops with herbicides on windy days and when temperatures are over 70 degrees Fahrenheit.
Ask neighbors to consider using herbicides the first part of March, before grapevines come out of dormancy. Good relationships with neighbors, well-established throughout the year, go a long way toward gaining cooperation in preventing herbicidal damage to grapevines.