I attended a class recently, for landscape industry professionals, and heard some excellent advice for managing disease and insect problems in your yard. The two speakers I heard are part of the lead team at the UW-Extension Plant Disease Diagnostic Clinic in Madison.
The first speaker, Phil Peletari (Insect Diagnostic Lab, http://www.entomology.wisc.edu/diaglab), spoke about insect response to environmental stress. His focus was on how insects respond to environmental changes and how stressed plants respond to insect pests.
The changing environment, both annually and over long periods of time, impact the health and survivability of both plants and insects. Pretty basic knowledge. The changing environment can apply to us as well if we think in terms of food resources, water resources, or even monetary resources to heat and/or cool our homes.
He stated the number one stress factor that impact insect numbers is food. If food resources are high, more plants to feed on, the insects will do well and numbers will rise. If food resources are low, insects will do poorly and numbers will decline. Other stress factors that impact insect success are extreme cold and heat at critical life stages, disease, and natural enemies (mostly other insects).
The number one stress factor for plants is drought or to little water. Other things which cause poor plant health are insect defoliation at critical stages of plant growth, wounds that allow diseases and insects to attack vital plant parts, compacted soils from construction, poorly chosen planting sites, incorrect use of chemicals (insect and weed control chemicals), climate change, and plant competition. These stresses can lead to higher disease rates and increased insect damage due to the reduced ability of the plant to respond to assaults on its health.
The second speaker was Brian Hudelson (UW Plant Disease Diagnostic Lab http://pddc.wisc.edu/staff.html). He shared information about disease problems with evergreens, though he stated these same diseases also effect most other plants. He explained that conditions causing high plant stress allow diseases to take hold and spread. These are many of the factors that can cause extreme plant stress; drought or flooding, extreme cold, high numbers of insects feeding on the plant, overcrowding of plants, over fertilization (particularly nitrogen), and pruning at stages of plant development which cause excessive growth.
Basically, plants under extreme stress are more prone to being attacked by disease and insect pests. These following recommendations will help you create an environment for happy plants and a more successful gardening experience.
- Keep your plants adequately watered. Give newly planted trees and shrubs 2″ of water per week, including rainfall. Established trees and shrubs need 1″ of water per week. Evergreens require appropriate watering until the ground freezes or we receive the first snowfall. This will help protect them from drying out in the winter.
- Plant the right plant in the right location. Make sure sensitive plants are placed in a protected area. For example, next to a building or house or in a sheltered garden space, out of the direct wind and cold. Many plants are salt sensitive, do not plant those near areas you will use de-icers in the winter. Some plants like it wet, place them in areas that have well drained, moist soils.
- Choose plants that are disease and/or pest resistant. We have many to choose from.
- DO NOT apply herbicides on or near plants you want to keep in your garden or yard. Herbicides that come into contact with your plants may cause severe damage, increasing stress, and eventual death. Some lawn care herbicides may also impact the plants you cherish, specifically 2,4-D and Dicamba.
- Fall mulching will help insulate your plants through the winter. If you have sandy soils, recommended mulch depth is no more than 4″. If you have clay soil, recommended mulch depth is 2″, maximum.
- When pruning plants, particularly infected plants, disinfect cutting tools with a 70% alcohol solution or over the counter spray disinfectant.
- Do not over fertilize. High nitrogen (N) application causes excessive new plant growth. The increased growth reduces energy the plant can put into fighting disease.
- Feed your soils. Healthy soil is full of organisms; small animals, worms, insects and microbes that thrive when the other soil elements are in balance. These organisms are essential for plant growth. They help convert organic matter and soil minerals into the vitamins, hormones, disease-suppressing compounds and nutrients that plants need to grow. Healthy soils will create an environment for healthy plants.
Here is a link that will give additional advice about gardening in Wisconsin, http://pddc.wisc.edu/staff.html.