Weed Control in Bearing Grape

INTRODUCTION
Herbicides are an important component of a comprehensive weed control regimen, especially in perennial crops such as grape. Herbicides and weed control should be the least time consuming of all the pest management practices in grape growing. Universities continue to evaluate new and improved herbicides for potential use in grapes. In order to add more herbicides to the arsenal available for growers, an experiment was conducted in 2006 to compare the performance of a new unregistered pesticide to various labeled herbicides.

MATERIALS AND METHODS
The experiment was initiated in spring of 2006. Herbicides were applied using a CO2-pressurized backpack sprayer with a 2-nozzle shielded boom calibrated to spray a 3 ft band at 30 psi and a 3 mph walking speed. The 11002-nozzles were set at 7 inches above ground to obtain good spray overlap and complete weed coverage. The spray boom was moved in and out in the tree row to avoid spraying the vine trunks. Therefore, weeds on the base of vine trunks were taller throughout the season and did not reflect the effectiveness of the applied herbicide.

Plots were 6 ft x 60 ft long. The experimental design consisted of a randomized complete block with three replications.

The preemergence (PRE) treatments were applied on 26 April 2006. Grapes were at the 0.5-2" green tip stage. As weeds had been growing since early March and were 3-4 inches tall, Roundup WeatherMax at 24 oz/A (1 lb ai/A) was included with all treatments. All treatments were applied early in the morning with average wind speed of 2.5 mph.

No yield data was collected from this experiment as this was not the original intent. Only visual weed control ratings were collected at various dates. The scale used in these ratings were on a 1-10 scale, with 1 = no control and 10 = complete kill or no weeds present. A rating of 7 (70-75% control) or more is considered a commercially acceptable value.

DAND = dandelion; LACG = large crabgrass; HONE = horsenettle, HVMW = honeyvine milkweed.

			HONE	HVMW	LACG	DAND	LACG	HONE	HVMW
Trt	Treatment	Rate	RATING	RATING	RATING	RATING	RATING	RATING	RATING
No.	Name	lb ai/A	28 DAT	28 DAT	28 DAT	28 DAT	75 DAT	75 DAT	75 DAT
1	Untreated Control	-	6 a	6 de	6 a	3 b	1 e	1 h	1 d
	Roundup	1
2	Chateau	0.375	10 a	10 a	10 a	10 a	10 a	3 e	5 d
3	Prowl	2	5 a	6 cde	10 a	10 a	7 d	1 gh	1 d
4	V-10142	0.5	7 a	9 abc	10 a	10 a	2 e	8 b	2 c
5	V-10142	1	6 a	8 a-d	10 a	10 a	1 e	9 a	7 a
6	SURFLAN	3	7 a	7 b-e	9 a	10 a	9 bc	1 a	1 d
7	PRINCEP	2	7 a	4 e	10 a	10 a	9 b	1 a	1 d
8	KARMEX	2	7 a	5 e	10 a	10 a	10 a	8 b	1 d
9	CHATEAU	0.375	10 a	10 a	9 a	10 a	8 cd	2 fg	3 c
	PROWL	2
10	CHATEAU	0.375	10 a	10 a	10 a	10 a	10 a	4 d	7 a
	V-10142	0.5
11	CHATEAU	0.375	10 a	10 a	10 a	10 a	10 a	7 c	7 a
	V-10142	1
12	CHATEAU	0.375	10 a	10 a	10 a	10 a	10 a	9 ab	4 b
	SURFLAN	3
13	CHATEAU	0.375	7 a	9 ab	10 a	10 a	9 b	5 d	5 b
	PRINCEP	2
14	CHATEAU	0.375	10 a	10 a	10 a	10 a	8 bc	3 ef	5 b
	KARMEX	2
LSD (P=.05)			4.8	2.8	2.2	1.6	0.7	0.7	0.7
Standard Deviation			2.9	1.6	1.3	1.0	0.4	0.4	0.4
Means within columns followed by the same letter are not statistically different at P=5%.

At 28 day after application, plots were much cleaner compared to rows adjacent to, but not part of, the experiment.

The new herbicide evaluated this year was V-10142, not yet labeled for use in grape. It was tested at two rates (0.5 and 1 lb ai) alone and in combinations with Chateau. Of the individual herbicide treatments (treatments 2-8), Chateau had 100% kill of all weeds at 28 and 75 DAT, except for horsenettle and honeyvine milkweed with 30% and 50%, respectively. At 28 DAT, V-10142 at either rate was similar in weed control effectiveness to Chateau (treatment 1) and Surflan (treatment 6), with ratings ranging from 7-10. Chateau combination with five other preemergence herbicides (trts 9-14) performed equally at 28 DAT, except for Chateau + Princep combination which was a little weak on horsenettle. At 75 DAT, only the high rate of V-10142 (treatment 5) had better honeyvine milkweed control with 70-75% kill. All other treatments had lost their honeyvine milkweed control efficacy by that date.

It is encouraging to see that three perennial weeds, namely honeyvine milkweed, horsenettle, and dandelion were 100% controlled with treatments 9-14. By 75 DAT, treatments 11 and 12 (Chateau+ V-10142, and Chateau + Surflan, respectively) had 70-90% control of horsenettle and treatments 10 and 11 (Chateau+ V-10142 at both rates) had 70% control of honeyvine milkweed and are considered the best treatments. All other combination treatments ranged from 30-50% control efficacy.

For the individual herbicide treatments (trts 2-8), V-10142 1 lb ai/A was comparable to Chateau 0.375 lb ai/A (high end of the labeled rate) in residual control of honeyvine milkweed, with control efficacy of 50-70%. However, only V-10142 (low and high rates) had any significant residual control of horsenettle at 75 DAT, with ratings of 80-90% control.