How to protect potato tubers from phytophthora during late summer

Yellowing foliage and wilting potato stems in August often lead gardeners to harvest prematurely. However, rushing the process can result in significant losses during winter storage if the tubers are not physiologically ready. The primary indicator for harvesting is not a calendar date, but the maturity of the tuber skin.

Determining Harvest Readiness

Environmental conditions vary annually, making fixed dates unreliable. To determine if potatoes are ready for mass harvest, gardeners should observe the plants: look for noticeable wilting and yellowing of the lower leaves.

To verify maturity, dig up a single plant and rub a tuber with a finger. If the skin is thick and remains intact, the crop is ready. If the skin is thin and peels away easily, harvesting should be delayed by one week.

Managing Late Blight (Phytophthora)

The appearance of characteristic dark spots on leaves in late summer indicates phytophthora. If the infection is limited to the greens, the harvest can still be saved by preventing fungal spores from reaching the tubers via rain.

In this case, gardeners must remove all foliage immediately by mowing it and burning the debris or removing it from the plot. The tubers should remain in the soil for another 7–10 days to allow the skin to thicken and break the connection with infected residues.

Phytopathologist Natalya Drozdova notes that once the foliage is removed, the potatoes are effectively "preserved" in the soil, which is a critical stage for forming the protective layer required for winter survival.

The Curing Period and Storage Preparation

To ensure long-term storage, tubers must undergo a curing period rather than being moved directly into a damp cellar. Potatoes should be placed in a well-ventilated area—such as a shed or under a canopy—out of direct sunlight to avoid greening and the accumulation of solanine.

Before loading the harvest, storage rooms should be ventilated and potentially whitewashed with lime for disinfection.

Sorting for Long-Term Storage

Tubers must be divided into fractions before storage. Those with depressed dark spots, signs of scab, or tool cuts must not be stored with the main batch, as one infected potato can trigger a chain reaction of rot in the entire container.

Damaged but otherwise healthy tubers should be set aside for immediate consumption. Only firm, clean specimens are suitable for wintering.

Olga Semenova, an agronomic consultant for gardeners, emphasizes the importance of inspecting the "eyes" and general shape during sorting, as abnormalities can indicate variety degeneration or hidden defects that may surface after a month in storage.

Questions about Potato Storage

How long should potatoes dry outdoors?

In dry weather, 2–4 hours directly on the garden bed is sufficient to dry the soil. This is followed by a curing period under a canopy for 7 to 10 days to ensure the skin has fully healed.

Can potatoes be washed before storage?

This is only advisable if every tuber can be dried perfectly. Excess moisture in the cellar promotes fungal growth; therefore, it is safer to gently remove dry soil by hand using gloves.

What happens if potatoes are harvested too early?

Thin skin cannot retain internal moisture, leading to shriveled and wrinkled tubers. Additionally, such potatoes are highly susceptible to mechanical damage during transport.

Should foliage be cut from healthy plants?

Yes. Removing the greens one week prior to harvest stimulates the flow of nutrients from the stems into the tubers and accelerates the maturation of the protective skin layer.

Source: This article was adapted from an original Russian-language publication by Pravda.Ru.