Losses due to disease have been estimated to be as high as 50% in Brazil and some African countries. Losses in India have fluctuated between 7% and 20% and in the USA have been reported as high as 15%. One widespread disease is bacterial, known as angular leaf spot, and in African countries this is the most serious disease. Fungus diseases which attack the growing cotton plant include fusarium and verticillium wilt and Texas root rot. Fusarium wilt is an important disease in the USA and the major disease in Egypt. Texas root rot is limited in distribution to areas of Mexico and the USA. Of the insect pests, the pink bollworm is the most widely distributed. It has become established in the 8 the countries that produce 90% of the world's cotton. In the USSR, it has caused severe losses. In India and Egypt the average annual loss caused by pink bollworm is between 15 and 25% and in Brazil, between 20 and 25%. It is the most serious cotton pest in China. The most serious cotton pest in the USA is the boll weevil. It is restricted to North and Central America, but another closely related species occurs in South America. Insects which feed on the leaves and buds, including the cotton leafworm and the sucking insects (fleahoppers, leafhoppers and aphids), do considerable damage to crops throughout the world. Of the weed pests, the most severe and widespread are cyperus rotundus, cynodon dactylon, and portulaca oleracea.
In China, the main cotton pest is the boll weevil - also a danger to cotton crops in other countries. Efforts to develop new methods of biological control have a certain urgency, because farmers and scientists are increasingly troubled by the costs and dangers of chemicals pesticide use. The University of Hubei in China, looking for natural predators to control cotton pests, found that of 600 predators, more than 100 were varieties of spiders. By maintaining populations of spiders in their fields, farmers find that their crop yields increase. At the same time, they have cut down on chemical use by 80%.
In 1889, California orange growers were losing their crops to a bug known as the cottony cushion scale. They successfully responded by enlisting the help of a small but hungry insect recently arrived from Australia, the seven-spotted ladybug.