Late Season Weed Control in Apple and Peach - UKREC - 2003
Joseph Masabni, Department of Horticulture, Princeton, KY

Introduction

In the continuing efforts to serve the Kentucky State Horticultural Society, two weed control experiments were conducted in 2003 to test labeled and experimental herbicides on apple and peach. The experimental herbicide (Chateau 51WDG) is not yet labeled on apple and peach, and must not be used as this is against federal law. The purpose of testing this herbicide is to collect data to support its registration, in the case of its proven effectiveness.

Two experiments were conducted at the University of Kentucky Research and Education Center (UKREC) in Princeton, KY. The purpose of these 2 experiments is to test the effectiveness of preemergence herbicides on apple and peach and how their performance is enhanced with the addition of a new non-labeled preemergence herbicide.

The experimental design used for both experiments was a randomized complete block design with 3 replications.

Apple: The apple planting was established in 1997. The variety in this experiment is Golden Delicious on M.9 rootstock. Trees were spaced 8 ft within rows 16 ft apart. At the time of herbicide application, trees were of mature age, in good overall condition, and have been bearing for at least 3-4 years. Each replication consisted of 3 trees for a total of 24 ft of row per treatment. Herbicide treatments were applied using a 4 8002-nozzle boom backpack sprayer set at 30 psi and 20 GPA with a 5.3 ft spray swath width. Sprays were applied on both sides of the trees for a total width of about 10 ft per treatment. Whenever possible, sprays were meant to completely cover the plots and no effort was made to avoid spraying tree trunks. Sprays were applied on May 16, 2003. By this date, spring weeds have already germinated. Therefore, the day prior to herbicide application, the orchard was mowed to remove as many weeds as possible. In addition, Roundup WeatherMax (1 lb ai/A) was tank mixed with all treatments to further control existing weeds. The untreated control treatment consisted of a one time application of Roundup WeatherMax.

Peach: The peach planting was established in 1994. The variety in this experiment is Redhaven on a number of rootstocks. Trees were spaced 16 ft within rows 18 ft apart. At the time of herbicide application, trees were of mature age, in good overall condition, and have been bearing for at least 5-6 years. Each replication consisted of 2 trees for a total of 32 ft of row per treatment. Herbicide treatments were applied using a 4 8002-nozzle boom backpack sprayer set at 30 psi and 20 GPA with a 5.3 ft spray swath width. Sprays were applied on both sides of the trees for a total width of about 10 ft per treatment. Whenever possible, sprays were meant to completely cover the plots and no effort was made to avoid spraying the tree trunks. Sprays were applied on May 21, 2003. As with the apple experiment, mowing and tank mixing Roundup WeatherMax with all treatments was necessary to control existing weeds. The untreated control treatment consisted of a one time application of Roundup WeatherMax.

The same herbicide treatments were used for both the apple and peach experiments. The only difference is the higher rate of Sinbar in treatment 3 in peach than in apple (1 lb ai/A in peach and 0.75 lb ai/A in apple).

The experimental herbicide, Chateau 51 WDG, is currently labeled by Valent for the preemergence and postemergence control of certain weeds in peanut and soybean. In previous studies, it has shown significant weed control effectiveness and a long period of activity, which is the reason why it was included in this experiment.

For both experiments, weed control effectiveness were determined by a visual injury ratings using a scale of 1 – 10, with 1 equivalent to no injury or similar to the control plot, and 10 equivalent to complete kill or none present.

The following are abbreviations used in the tables below: DAT = days after treatment; PRE = preemergence weed control; WHCL = white clover; MATE = marestail; LACG = large crabgrass; DAND = dandelion; COCO = common cocklebur; HONE = horse nettle; NLPL = narrowleaf plantain.

Apple:

Table 1 shows the weed control ratings taken at 32 days after treatment of 3 weeds found in the Golden Delicious apple block. No honeyvine milkweed or ivy leaf morningglory vines were present in this experiment, even in untreated plots. Table 1 shows that all herbicide treatments that included a preemergence herbicide had better weed control than those plots treated only with the non-selective contact herbicide Gramoxone Extra.

All plots treated with both low and high rates of Chateau had absolutely no weeds re-germinating. On the other hand, plots of treatments 2 or 3, showed a flush of newly germinating seedlings, similar to those of the control plots. The majority of the weeds germinating were chickweed, pigweed, and large crabgrass. No significant differences were observed in the performance of Chateau when applied at low (0.38 lb ai/A) or high (0.75 lb ai/A) rates.

Table 1. Weed control ratings taken 32 days after treatments in Golden Delicious apple.

Roundup WeatherMax 1 lb ai/A was included with all treatments to control existing weeds.
Gramoxone Extra in treatment 12 was applied twice.

Peach:

Results of weed control in peach mirrored those observed in apple. Weed regrowth was not observed in any plots treated with either low or high rates of Chateau. In general, weed control at 26 days after treatment was generally better for most weeds in treatments that included Chateau. In specific, dandelion control was about 30-40% better when treated with a Chateau and Devrinol mix compared to a Sinbar and Devrinol mix. This difference in weed control effectiveness was less evident for other weeds rated in this experiment.

Honeyvine milkweed vines were present in this peach block. Not enough vines were present in the control plots to allow for data to be collected for them. Instead, plots were rated for the presence (or lack) of this weed. We observed that all plots treated with Chateau had no honeyvine milkweed vines re-germination. The only exception is one replication of treatment 5, which included Chateau (low rate) and Devrinol, where some vine re-germination was observed. The other 2 replications had no vine re-germination.

On July 13, 2003, a commercial apple IPM meeting was held at UKREC in Princeton, KY. Attendees of this meeting had a chance to visit the orchard and compare the results of the weed control experiments in apple and peach. At this date, 73 days after treatments, few weeds were observed in the plots treated with Chateau in the spray mix. Next in long-term residual control were the plots treated with Sinbar and Karmex mix (treatment 2). Plots treated with Sinbar and Devrinol were the poorest and thus had the highest number of newly germinated weeds.

Table 2. Weed control ratings taken 26 days after treatments in Redhaven peach.