• Phytophthora crown rot (Phytophthora parasitica): A brown, wet discoloration develops at the center of plants, which wilt and collapse completely. Laboratory diagnosis may be necessary to determine whether this browning and collapse is caused by fungus infection or tomato spotted wilt virus.
• Impatiens necrotic spot and tomato spotted wilt tospoviruses: On the most susceptible young plants (four to six weeks old), browning and total collapse is typical. On more mature plants, look on the older leaves for round brown spots, chlorotic ring spots, or brown zigzag patterns. Control of the vector, the western flower thrips, is essential to halt the spread of the virus to other crops.
• Foliar nematode (Aphelenchoides spp.): Necrotic leaf lesions, which progress until the whole leaf is destroyed.