Why Improve Weed Management in Young Trees?

The investment in a new orchard is large, and poor weed management can reduce the performance of a new orchard for many years. Planning your weed management strategy for the planting year, as well as the following seasons, is an important step in getting the most out of your investment.

Although most growers have a large dislike for weeds in general, it is important to understand the "enemy" and to focus efforts and expense to manage them for the biggest return.

Planting new orchards requires time and labour when orchard growers are busiest- usually the spring - and controlling weeds after planting may become a low priority. We have all heaved a sigh of relief as the last tree is tamped in, and we rush off to catch up on other orchard work. But this is exactly when we should be focusing efforts on keeping weed competition down.

The Goal: Weed scientists have been working to identify the Critical Weed-free Period for each crop. For annual crops this time is early in the season and surprisingly short. This concept is easy - if a crop is kept weed-free during its Critical Period, no yield reduction from weeds will result. Weeds growing within the crop before and/or after this Critical Period will not affect yields.

In perennial crops like fruit trees, the "yield" effect may not be apparent in the first year. But research has shown a direct effect between tree growth in the first year, and yields in each of the subsequent years. The economics of new orchard plantings show that yields early in the orchard life are much more valuable than yields later in the life of the orchard.

As growers, we recognize that there may be reasons other than yield to control weeds at other times eg. to facilitate harvest or to attract PYO customers. But to maximize your dollar return in yield, weeds need to be controlled only for this short period.

Critical Weed Free Period in Fruit Trees: Research by Dr. Ian Merwin at Cornell University has shown the effects of weeds in new orchards. In a Gala/M26 planting, first cropping 2 years after planting, yields were much larger when weeds were controlled early (May) in the planting year, and as well, when weeds were controlled longer (May to July) in the planting year. Weed competition occurred even under a full trickle irrigation schedule. Note that these yield effects were measured 2 years after the weed competition occurred!

Figure 1. Effect on Trunk Cross-Sectional Area in Newly Planted Gala/M26 Apple

Link to Data Equivalent Chart

Early weed competition will also have an effect on fruit size. In Dr. Merwin's research with Gala (where size can be a concern), controlling weeds during May and June, as well as during the preharvest month of August, gave better fruit size in the first crop year - again, 2 years after the weed competition occurred.

Figure 2. Yield Effects from 1st Year Weed Control

Link to Data Equivalent Chart

The strategy: Once we recognize the importance of controlling weeds during the Critical Weed-free Period, we can begin planning how to achieve the weed management needed. Watch for a series of articles in this season's newsletters to outline practical steps to achieve the weed management you need.

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