Gardeners are wondering if they are going to get a crop of red, ripe tomatoes because of rains across the state states University of Illinois Horticulture Educator, Kelly Allsup. If you suspect disease, here are few signs to look for and what you can do about it:
Septoria leaf spot is the most common of all the tomato diseases. The disease symptoms begin mid to late summer and start off as dark leaf spot the same size as a pencil tip, surrounded by a yellow halo. The smaller spots advance to dark brown lesions with a purple border and lighter colored centers. This fungal disease attacks leaves, stems and sepals (outer leaves of the flower) and spares the fruit. However, diseased and damaged leaves can cause fruit abortion and expose fruit to sun-scald.
Early blight's initial symptoms are small, dark, round spots (larger than Septoria leaf spots) that advance to reveal dark brown concentric lesions. The fungal disease causes yellowing, dead leaf edges and leaf drop. Leaves, stems and fruit are affected. The fruit has the same concentric ridges, which look like leather. This disease starts on the seeds or transplants. In addition to tomatoes, peppers, and eggplant can be infected.
To control leaf spot diseases on tomatoes, horticulturists recommend a 2- to 3-year crop rotation when the disease has been detected and removing infected plants to prevent further spread.
Good cultural practices are proper plant spacing and staking to ensure good air movement, reducing humidity by removing weeds, and mulching the soil. To prevent spread, do not work in the garden while the plants are wet.
Fungal pathogens can live in the soil for three to four years. All plant debris must be composted or tilled into the soil. All stakes and garden tools must be disinfected with alcohol or bleach solution. Leaf spots can infect seeds so always find reputable sources of seeds.
If fungicide sprays are going to be utilized, use them as a preventative treatment. Before deciding to do a curative spray, understand that leaf loss can be 50 percent before there will be a loss in yield. To further prevent the spread, University of Illinois recommends a weekly spray of chemicals with the following active ingredients: chlorothalonil, copper, mancozeb and Maneb. These names will be on the label of the chemicals. Be sure to read the label and follow instructions exactly to achieve optimal control.