Articles
EFFECT OF FUNGICIDES AND TIMING OF APPLICATION ON THE CONTROL OF POWDERY MILDEW (PODOSPHAERA LEUCOTRICHA), YIELD AND FRUIT QUALITY OF APPLES.
The most rapid disease development occurred during a 4–6-week period starting at tight cluster-pink stage and peaking when fruits were 20–30 mm in diameter at which time 80 % secondary leaf attack was observed in untreated plots.
With a low amount of primary inoculum, some delay in the disease progress was noted.
Unsprayed trees showed a high level of leaf and bud infections at the end of the season independent of the amount of primary inoculum.
Based on this information the optimal application timing of penconazole (TOPAS®) for powdery mildew control was investigated in comparison to sulfur or dinocap and some other sterol inhibitor compounds.
Penconazole at 2.5 g a.i./hl reduced sporulation of primary infections by 60–90 % when applied 2–3 times at 10-day intervals, starting at tight cluster.
Sulfur at 480 g a.i./hl gave less than 10 % anti-sporulant activity and such plots required, therefore, significant more manpower for cutting off primary infected shoots.
Cover sprays with penconazole 2.5 g a.i./hl at 14–18-day intervals provided 90–98 % control of secondary leaf attack and bud infections.
Sulfur at 240 g a.i./hl or dinocap at 30 g a.i./hl provided 66 % control of secondary attack with low primary inoculum but only 30 % with high levels of primary inoculum.
Penconazole was able to provide good to excellent control when applied after disease levels had reached 5 and 10 % secondary infection.
It is, however, important to carry out the first spray before full bloom to obtain fruit protection.
A first spray at the end of blossom was already too late and could not prevent serious fruit attack.
In situations where disease was kept low by applying penconazole from tight cluster through to about 30 mm fruit size, even weak compounds like sulfur could be used to maintain the protection till the end of the terminal growth period.
Trial results also show the devastating influence powdery mildew can have on fruit production.
After 3 years, penconazole treated trees yielded 40 % more than sulfur treated plots and 7 times more than untreated plots.
Several years of experience indicate the optimal timing for powdery mildew control with penconazole to be from tight cluster through to at least 30 mm fruit size and a spray interval of 10–18 days.