Water is key to potato rust spot
10 March 2000
Water is key to potato rust spot
REDUCING irrigation interval on potatoes seems the key to cutting internal rust spots, according to UAP trials.
"Water management is by far and away the most important means of minimising internal rust spots," says potato specialist Barrie Florendine.
In three trials Estima was irrigated so tensiometer readings did not exceed -0.3 bar, equivalent to a soil moisture deficit of 25mm (1 in). Internal rust spots were cut by 69%, more than any other control method in the trials (see table).
Most control methods concentrate on increasing calcium supply to the tubers, as rust spot is often associated with low calcium. But applying 2.5-4t/ha (1-1.5t/acre) of Gypsum (calcium sulphate) presents logistical problems and the fertiliser manufacturers preferred option of applying up to 500kg/ha (4cwt/acre) of calcium nitrate means cutting back seed-bed fertiliser to allow for the extra nitrogen.
"And there was no response to any of the foliar applied products. None of them increased tuber calcium, adding to the evidence that calcium and boron do not travel downhill."
RUST SPOT REDUCTION
Input % reduction
Irrigation 69
Gypsum 59
Ca(NO3)2 52
Late planting 47
Mean of UAP trials.
Input % reduction
Irrigation 69
Gypsum 59
Calcium nitrate 52
Late planting 47
Mean of UAP trials.
A bit more management input to cut irrigation intervals can reduce internal rust spots, says UAPs Barrie Florendine.