Weed Management
As I walk through orchards in the state, including our own research orchards at the UVM Horticulture Research Center, one area of pest management practices that is often lacking is that of weed management.  We know that weeds compete for nutrients, water, and light. In addition, some weeds, such as white clover, wild carrot, and dandelion, can be reservoirs of the tomato ring spot virus which can be transmitted to apples and reduce tree vigor and yield.  In order for growers to invest more time and resources in weed control, it is necessary to demonstrate that the control of weeds in an orchard is cost efficient, both in economic and environmental terms.
A weed by an IPM definition is a 'non-harvested plant that significantly reduces crop yield and or quality by competing for essential resources such as nutrients, water, or sunlight without providing for compensatory benefits'.
There have been many studies conducted in orchards that demonstrate that weeds have a direct effect on tree growth.  One such study conducted in New York demonstrated that the complete elimination of weeds in a 6-foot wide area around the tree increased shoot growth by 38% when compared to trees with no weed control (see Table 1).Table 1.  Total shoot growth of apple trees during first year in relation to the percent of weed control within a 6-foot wide row strip (Integrated weed and soil management in fruit plantings,  CCE Information bulletin 242) Table 1.  Total shoot growth of apple trees during first year in relation to the percent of weed control within a 6-foot wide row strip (Integrated weed and soil management in fruit plantings,  CCE Information bulletin 242)

In another study conducted in Washington State (1990) on seven-year old Golden and Red Delicious apples, it was concluded that the control of weeds had a pronounced effect on tree growth (shoot extension, leaf size, trunk growth), fruit size, leaf nitrogen (N), and fruit production (Raese, 1990).  In addition, it was concluded that supplemental N overcame the effects of poor weed control, but increased the incidence of bitter pit in 'Red Delicious' and increase the potential for ground water contamination.
Another study also conducted in NY estimated, for three years (1993-1995), the ratio of harvested crop value to yearly weed control in a newly planted orchard.  This study demonstrated that a 2 meter square weed-free area around the tree has the best ratio of harvested crop value to yearly weed control (Figure 1)
Another study also conducted in NY estimated, for three years (1993-1995), the ratio of harvested crop value to yearly weed control in a newly planted orchard.  This study demonstrated that a 2 meter square weed-free area around the tree has the best ratio of harvested crop value to yearly weed control (Figure 1)

Merwin and Stiles (1994) conducted a very extensive study where various conventional and alternative orchard ground cover management were compared for six years during the establishment of an orchard in Ithaca, NY  The following are some of their conclusions from this study.

• Trunk cross-sectional area and fruit yield were higher under hay-straw mulch, post-emergence herbicides, and pre-emergence conditions; intermediate under tilled conditions; and lowest under chemically growth-regulated sodgrass, close-mowed and crownvetch conditions (see Table 3)
  
• Soil concentrations of K, P, and B were  greater under hay-straw (see Table 4).  This system had excellent tree growth, nutrient uptake and fruit yield.  However, this system was the most expensive to establish and maintain.  Tree mortality due to Phytophthora and meadow  voles were very high.
  
• The crownvetch was difficult to establish, failed to increase N availability to the trees,  and exacerbated meadow vole problems.
  

2. Herbicides can damage trees.  Know  what herbicides can be used on what trees and at what age ( see Table 21 Herbicide Options for Different Tree Ages on page 97 of the NE Pest Management Guide or attached copy of Table 45 from The 1998-1999 Pennsylvania Tree Fruit Production Guide (http://www.cas.psu.edu/docs/CASDEPT/hort/TFPG/part4/table45.htm)
   
3. Resistance to herbicides can build up
   
4. Know your weeds to determine which herbicide will be the most efficacious to use (see Table 20  Type of Weeds Controlled by Herbicides on page 96 of the NE Pest management guide, or see attached copy of Table 45 from The 1998-1999 Pennsylvania Tree Fruit Production Guide (http://www.cas.psu.edu/docs/CASDEPT/hort/TFPG/part4/table46.htm)
   
5. Timing of application is very important
   
6. Leaching and runoff can be a problem
   
7. Always use the correct rate
   
8. Always read  and follow the label because THE LABEL IS THE LAW