Evaluation of Herbicide Performa

Introduction
An experiment was initiated in 2006 to evaluate the safety and performance of non-registered herbicides in newly-planted pawpaw seedlings. Currently, only Roundup, Gramoxone, and Aim are labeled for pawpaw plantings. All three herbicides are postemergent and must be applied with shielded booms as a directed spray while avoiding spraying green leaf or trunk tissue. More herbicides labeled for use in pawpaw are needed, especially with preemergence activity.

Materials and Methods
One-year old seedlings were hand transplanted on June 7, 2006 at a 2 ft spacing between plants. The experimental design consisted of 13 treatments with 3 replications, with 2-3 plants per replication. The experiment was set up as a randomized complete block design. Treatments were applied on June 13, 2006 using a CO₂-pressured backpack sprayer with a 1-nozzle FF8004 boom set to deliver 20 gpa at 30 psi. The nozzle was set to spray a 3 ft band on either side of the planted row for a total plot width of 6 ft. The nozzle was also set to spray the bottom 6-8 inches of the trunks. This was to evaluate the injury potential from direct herbicide application on the seedlings, in addition to any possible injury through root absorption.

On the day of application, it was noted that some leaves showed sunburn injury, which is not related to any herbicide application. The weather condition at the time of application are as follows:

Results and Discussion
Table 1 lists the 13 herbicide treatments and their effects on the pawpaw transplants’ season-long increase of total leaf number, total branch length (cm), and total plant height, and percent plant survival by 57 days after treatment (DAT). The most obvious observation is that none of the herbicides killed all of the transplants. Only three herbicides (treatments 2, 3, and 4) resulted in reduced plant survival, but not statistically different from the control treatment. Treatments 2, 3, and 4 also resulted in reduced plant growth for all the measured variables.

The best treatment was Solicam at 4 lb ai/A, which resulted in plant growth exceeding even the untreated control plots. The worst treatment was Prowl at 0.412 lb ai/A, which resulted in significantly less developed leaves counted at the end of experiment. It is also worthwhile noting that even Prowl was worse than Roundup and Gramoxone, two non-selective herbicides that are effective in killing any green tissue they contact. It is reasonable to assume that the 1-year old pawpaw transplants must have enough bark formation to tolerate direct application of these two herbicides.

It is also worth noting that all preemergence herbicides (Princep, Gallery, Karmex, Surflan, Chateau, Solicam, and V-10142) appear to have potential application in newly-transplanted pawpaw plantings.

Table 1. Effects of various herbicides on growth variables of newly-planted pawpaw trees.
Trt	Treatment		Increase in Leaf Number	Increase in Branch Length	Increase in Plant Height	Percent Survival
No.	Name	Rate	in 55 days	in 55 days (in.)	in 55 days (in.)	55 DAT
1	Untreated Control		38 a	13 a	30 a	100 a
2	Princep	10 pt/A	23 a	13 a	19 a	89 a
3	Gallery	21 oz/A	30 a	21 a	22 a	89 a
4	Karmex	6 lb/A	15 a	16 a	29 a	89 a
5	Surflan	12 pt/A	16 a	14 a	15 a	100 a
6	Chateau	12 oz/A	37a	19 a	30 a	100 a
7	Prowl	1 pt/A	12 a	7 a	17 a	100 a
8	Treflan	4 pt/A	30 a	15 a	22 a	100 a
9	Gramoxone Inteon	3 pt/A	32 a	19 a	24 a	100 a
10	Roundup	1 pt/A	22 a	12 a	24 a	100 a
11	Solicam	5 lb/A	48 a	19 a	33 a	100 a
12	Goal	6 pt/A	16 a	9 a	13 a	100 a
13	V-10142	6 pt/A	22 a	17 a	26 a	100 a
LSD (P=0.05)			26.4	11	14	15.9

Air Temp., Unit:	72^◦F
% Relative Humidity:	39
Wind Direction, mph:	N 3.5
Dew Presence (Y/N):	N
Soil Temp., Unit:	60^◦F
Soil Moisture:	moist
% Cloud Cover:	100