Weed Control in Pepper – Henderson County - 2005
Joseph Masabni, Joe Williams, Department of Horticulture, UKREC; Nathan Howard, Henderson Co. Extension Agent

An experiment was conducted in 2005 on row middles of transplanted peppers to quantify the effectiveness of labeled and non-labeled herbicides, which are commercially available but not for use on pepper yet.

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 3 mph walking speed. The 11002-nozzles were set at 7" above ground level to obtain good spray overlap and complete soil coverage.

Plots were 3 ft x 15 ft long. Both sides of each treatment bed were sprayed with the same treatment. Peppers were harvested from the treatment beds only. The beds that had different treatments applied on each side were not harvested as they were not part of this experiment. The experimental design consisted of a randomized complete block with 3 replications.

The preemergence (PRE) treatments were applied on 4 May 2005 immediately after transplanting. Weed pressure was minimal this year due to early spring rains followed by dry weather that crusted the soil surface and acted as a barrier against weed germination. Therefore, no weeds were present at time of PRE treatment application. The postemergence (POST) treatments were applied on 10 June 2005 when peppers fruits were in flower and plants 1-1.5 ft tall. All treatments were applied early in the morning with average wind speed of 2.5 mph. Gramoxone 5L 0.8 pt was included with all POST treatments to control germinated weeds at time of application.

In addition to currently labeled herbicides, this experiment also addressed non-labeled herbicides as part of our effort to support their future registration. Sandea is currently labeled on row middles in pepper. Readers are strongly reminded that experimental herbicides’ inclusion in this report is not a legal application in a commercial or residential setting and UK does not recommend their use until they are labeled. The reason I am listing the experimental herbicides here is because the intent of this experiment is their evaluation in the hope of their future registration. The 2 non-labeled herbicides were experimental herbicide A (treatment 4 POST, and treatment 9 PRE+POST) and experimental herbicide B (treatments 7,8 POST).

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. Yields, in terms of pepper number and weight, were collected over 2 weeks, until the grower decided not to harvest any more due to dropping prices. The grower applied ethylene to ripen the fruits and obtain uniformly red peppers.

The following is the full name of the weed codes used in the tables:

LACG = large crabgrass; RRPW = redroot pigweed; COLQ = common lambsquarters; BYGR = barnyardgrass.

Three weeks after PRE treatment, pepper plants were 6-8" tall with 12-14 leaves and flower buds forming. In terms of overall herbicide weed control ratings, T8 and T9 are the cleanest with no weeds present, followed by T7 and T2, followed by T1. LACG was about 1"-2" in T1 and 0.5" in T2. Plots with COLQ and RRPW had 1-2 plants/plot ranging in height from 0.5-3".

None of the treatments applied had any effect on the number of plants with an average of 25 plants per plot. Visual observation also didn’t indicate any herbicide injury to the plants. There was no quantifiable effect on the yield data. There was no significant differences in peppers numbers or yield/plot on either harvest dates. The general consensus after discussions with the grower is that this was not a typical year for weed germination and growth. The soil surface was hard and crusted for the whole duration of this experiment. This was due to excess spring rain followed by 2 weeks of hot sunny days that baked the ground into a hard surface.