Rusts, Blights, Wilts and Molds: Fungal Diseases From Wheat Field to Cacao Pod

Wheat Stripe Rust is a good opening because it shows how fast a fungal disease can move. Its spores travel on the wind, and a highly virulent race group first identified around 2000 spread across Europe, Central Asia and Africa, overcoming resistance genes bred into many popular wheat varieties.

Septoria Leaf Blotch is regarded as the most economically damaging foliar disease of wheat in Europe. Its lesson is about chemistry: it evolved resistance to the strobilurin fungicides during the 2000s, so managing resistance became part of control, not simply spraying.

Grey Leaf Spot of Corn shows how farming practice shapes disease. Narrow rectangular lesions limit the leaf area that fills the ears, and the disease grew in importance in the United States and sub-Saharan Africa from the 1990s as reduced tillage left infected residue on the soil surface.

Sclerotinia Stem Rot, also called white mold, attacks soybean, canola, sunflower, dry beans and hundreds of other broadleaf crops. It survives between crops as hard black sclerotia that can persist in soil for many years, which makes it a leading cause of yield loss in cool, humid seasons.

Verticillium Wilt lives in the soil and blocks the plant's water-conducting tissue. Its microsclerotia can survive over a decade without a host and no fungicide reliably cures an infected field, so growers lean on resistant varieties, long rotations and fumigation.

Gray Mold, caused by Botrytis cinerea, ruins flowers, fruit and stored produce and causes heavy postharvest losses. It is also the same fungus that winemakers deliberately encourage on ripening grapes as noble rot to make sweet wines such as Sauternes and Tokaji.

Powdery Mildew is a large group of related fungi that coat leaves, stems and fruit in white powder, on crops from cereals and grapes to cucurbits. Individual species are often host specific, but together they are among the most common and costly plant diseases in temperate and subtropical agriculture.

Downy Mildew is grouped with the fungal diseases in farming practice although the pathogens are oomycetes. Grape downy mildew, introduced to Europe from North America in the nineteenth century, prompted the development of Bordeaux mixture, one of the first widely used fungicides.

Coffee Wilt Disease moves the trail to tree crops. A vascular wilt caused by Fusarium xylarioides, it devastated robusta production in the Democratic Republic of the Congo in the 1920s and 1930s and again across Uganda, Tanzania and neighboring countries from the 1990s, and control relied on burning infected trees and replanting with resistant varieties.

Cacao Black Pod Disease closes the trail with the most economically damaging disease of cacao worldwide. It rots pods and the beans inside, can ruin a large share of a plantation crop within weeks under humid conditions, and is worst in West Africa, where the more aggressive Phytophthora megakarya predominates.