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

Table 1

Glasshouse trial: effect of foliar applications of 100 or 400 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)	Least square mean of disease cover score∗
	Powdery scab			Common scab
	RB	DE	Mean (rate)	RB	DE
0	0.50	0.83	𝟎.𝟔𝟔^a	0.16^bc	2.30^a
100	0.00	0.25	𝟎.𝟏𝟑^b	0.13^bc	1.10^b
400	0.03	0.00	𝟎.𝟎𝟏^b	0.05^c	1.10^b
Rate	(𝐹(2, 20) = 12.58, 𝑃=0.0003)			(𝐹(2, 20) = 5.64, 𝑃=0.012)
Variety	(𝐹(1, 20) = 2.71, 𝑃=0.115)			(𝐹(1, 20) = 60.31, 𝑃<0.0001)
Rate × variety	(𝐹(2, 20) = 0.92, 𝑃=0.416)			(𝐹(2, 20) = 4.48, 𝑃=0.025)

∗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.