Stems occasionally develop distinctly black areas or lesions and plants can be stunted. These pathogens are transmitted by the western flower thrips. Control of these diseases is focused on prevention since once plants are infected, they cannot be cured. It is important to eliminate and remove infected plants as soon as they are recognized and to eliminate other symptomatic plants since these viruses have very broad host ranges. It is also critical to manage the thrips population.
Plants appear unthrifty, small, and weak.
Above-ground symptoms are nonspecific as plants appear stunted, yellowed, and wilted. Diagnostic symptoms can be observed by the presence of galls on the roots. These can range in size from small swellings to large, distinctly clubby galls. The northern root-knot nematode, M. hapla , is a sedentary endoparasite, meaning that it infects host roots after hatching from eggs, stimulating the formation of a small gall containing specialized feeding cells, and feeds in the same location through several molts to produce several hundred offspring. Because most of its life cycle is inside roots, it may be spread to new locations with vegetative propagation material.