Agroforestry's potential impacts in vineyard integrated pest management efforts

In her 2021 Master's Thesis, Katherine Favor stipulated that "Agroforestry can benefit vineyards in many ways, both in terms of the above- and below-ground services that it provides to vineyard ecosystems. Agroforestry has been shown to affect below-ground parameters in vineyards positively by increasing drought resistance, reducing erosion, building organic matter, bettering soil structure, and improving vine rooting capability" and above-ground parameters by "... reducing pest and disease pressure, preventing wind damage and erosion, increasing stomatal aperture and leaf area, protecting against heat stress, and protecting against frost."

I have previously explored the aforementioned  below-ground services (water parameters, nutritional parameters, and grapevine rooting patterns) and now turn my attention to the above-ground services, beginning with pest and disease pressure.

Favor posits increasing vineyard pest and disease pressure (see below) and a significant role 

for agroforestry in combating the threat. Trees in the vineyard, she says, have the potential to reduce wind speeds (with impacts on insect, viral, bacterial, and fungal pathogen pressure), increase associated biodiversity (reducing dependence on chemical pesticides), and facilitating precision pesticide applications.

Improved Management of Insect Pests

As it relates to management of pests, many studies have shown that locating vineyards in close proximity to surrounding woody vegetation (surrounding biodiversity) or incorporating trees into vineyards (planned biodiversity) significantly reduces insect pest pressure. Agroforestry can also promote insect control through the provision of habitats for insectivorous animals such as bats.

The above benefits are offset somewhat by studies which show that windbreaks can increase the concentration of pest insects in downwind areas (flying insects prefer to settle in areas where wind speeds are lower than their flight speeds) but, overall, "the benefits of incorporating trees appear to outweigh their disadvantages" (Favor).

Viruses and Bacteria

There are 70 known virus species and three major bacterial diseases that can affect grapevines; and many of these are spread by insect vectors. There are no specific studies related to the impact of agroforestry systems on viruses and bacteria.

Improved Management Of Fungal Diseases

Fungal infections in vineyards is largely dependent on light, temperature, and humidity, factors which can all be modified by the presence of trees (Favor). For example, tree shade can reduce both the amount of heat and UV light reaching grapevines, with the potential for increased fungal development. No specific studies have been done in this area, however.

Powdery mildew is inhibited by high light intensity and enhanced under shade conditions; intercropping vines with trees, then, potentially increases the risk of powdery mildew infection. The potential for powdery mildew reduces with decreasing vigor of the vine, a situation that would occur if the vines and trees were in competition for resources.

Precision Pesticide Application

Windbreaks have been shown to reduce pesticide drift by between 80 and 90%, allowing for more precise timing of pesticide application at optimal levels even in the case of adverse wind speeds.

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