Foliar Treatments of 2,4-Dichlorophenoxyacetic Acid for Control of Common Scab in Potato Have Beneficial Effects on Powdery Scab Control

Table 2

Field trial number 1: effect of single or multiple foliar applications of 100 mg/L 2,4-D on plants of potato varieties Russet Burbank (RB) and Desiree (DE) on powdery scab and common scab severity.

2,4-D rate; (mg/L)	Application dates∗ (DAE)	Least square mean of disease cover score†
		Powdery scab			Common scab
		RB	DE	Mean (rate)	RB	DE	Mean (rate)
0	10, 20, 30	3.74	3.73	𝟑.𝟕𝟑^a	3.20	3.35	𝟑.𝟐𝟖^a
100	10	2.79	2.68	𝟐.𝟕𝟒^b	1.57	2.28	𝟏.𝟗𝟐^b
200 (2 × 100)	10, 20	2.70	2.57	𝟐.𝟔𝟒^b	1.48	2.24	𝟏.𝟖𝟏^b
300 (3 × 100)	10, 20, 30	2.63	2.73	𝟐.𝟔𝟖^b	1.35	2.25	𝟏.𝟖𝟎^b
Mean (variety)					𝟏.𝟗𝟎^b	𝟐.𝟓𝟎^a
Rate		(𝐹(3, 12) = 17.31, 𝑃=0.0004)			(𝐹(3, 12) = 38.63, 𝑃<0.0001)
Variety		(𝐹(1, 12) = 0.28, 𝑃=0.605)			(𝐹(1, 12) = 46.8, 𝑃<0.0001)
Rate × variety		(𝐹(3, 12) = 0.52, 𝑃=0.678)			(𝐹(3, 12) = 3.34, 𝑃=0.056)

∗Date (DAE) is the number of days after the average crop emergence.
†Disease cover score (0–6 scale [12]) assesses surface area of tubers covered with lesions. Percentage cover is the estimated percentage of tuber surface coverage derived from the disease cover score.
Treatment least square means with the same letter within individual disease columns are not significantly different at 𝑃=0.025 using the Tukey adjusted pairwise test.