BSPP ‘Plant Doctor’ Quiz #30 – September 2023

The correct answer is:

Late blight (Phytophthora infestans)

The classic necrosis surrounded by the white bloom of sporulation is clear in this photo. Powdery mildew is extremely rare on potatoes and is not typical of powdery mildews when it does occur and there is no downy mildew of potato (although Phytophthora is a close relative).

The correct answer is:

The one with black coloured antennae.

This is the famous Colorado beetle Leptinotarsa decemlineata an innocuous insect which only became a serious pest of potato when the potato was introduced to its native range.  The beetle with the tan antennae is the sunflower beetle Zygogramma exclamationis

Photo credit:  Marco Verch Black antennae beetle; Keith Roragen, Tan antennae beetle both Flickr

The correct answer is:

Nematode galls

These are galls on potatoes caused by Meloidogyne species.  The potato cyst nematode is a big problem in potato production but the cysts are tiny and on the side of the root (and all the same size)

The correct answer is:

Verticillium

The early symptoms of Verticillium dahliae infection are characterized by unilateral leaf yellowing. A wilt may develop but the leaves become necrotic as the disease progresses.

The correct answer is:

Bacterial infection:

Ralstonia solanacearum is a bacterial pathogen that frequently causes a rapid wilt.  The wilt is generally the first sign of disease, the plants will survive for several days (recovering from the wilt at night) before finally turning yellow and necrotic.

The correct answer is:

Herbicide damage:

Potatoes are difficult to kill with herbicides but these are the symptoms of low levels of Glyphosate on a potato volunteer.

The correct answer is:

Ignore them but they are reducing potato fruit production

They do a small amount of damage to the potato fruit which is beneficial to the grower as the fruits are not edible and are not harvested.

The correct answer is:

Mineral deficiency

Leaf distortion due to mineral deficiency is rare, even more so when that mineral is zinc. This is zinc deficiency in potato.

Photo credit:  Taken from  Nutrient Deficiencies of Field Crops: Guide to Diagnosis and Management Illustrated by Kumar, Prakash, Sharma, Manoj Kumar (ISBN: 9781780642789)

The correct answer is:

Mite feeding. 

The iron rust mite Polyphagotarsonemus latus feeding on potato causes what looks like iron rust.  The mites are too small to be seen as they are broad mites. It is a problem in the tropics and in temperate regions in glasshouses.

The correct answer is:

It may be possible to suggest PVY but not possible to make a firm diagnosis.

Field diagnoses can be accurate and precise but the symptoms of viral infection on potatoes can be tricky unless you are very experienced.  It should be possible to suggest that PVY is one of the potential causes.