Disease 1 - Spotted Tomato Wilt Virus

Disease - Spotted Tomato Wilt Virus

Spotted Tomato Wilt Virus identified in my vegie patch yesterday, affecting tomato heirloom variety "Principe Borghese."

First noticed shriveled, blackened leaves. On closer inspection of younger leaves, noticed brown, rust coloured spots, quite discreet and areas of larger yellow discolouration. Young fruit had started to drop off and some appeared shriveled. Only one plant out of six was affected and symptoms had come on quite rapidly. 

Host : 

wide host range, including ornamentals (eg. dahlia, nasturtium, petunia and zinnia), vegetables (eg. lettuce, celery, members of solanaceae family - tomato, eggplant, potato, capsicum), weeds (particularly solanaceous weeds eg. nightshade). 

symptoms :

start 14 - 21 days after infection. Disease recognizable by abnormalities on leaves. In tomatoes, small areas of bronzing in the terminal growth and upper surface of young leaves to eventually affect whole leaf, whilst in older leaves quite distinct bronze spots or rings between veins. Spots eventually extend and join up. Affected areas blacken and shrivel "as if they have been scorched by flames."  Leaf stalks and stems may develop brownish-black streaks, young fruit shrivel and fall. 

spread : 

by onion thrips, rarely by seed, not by contact between plants, not by pollen.

control : 

cultural methods - early planting increases severity, do not grow tomatoes next to flower crops or weeds which act as alternative hosts for onion thrips (eg. nightshade), plant excess plants to allow for losses. Most tomato varieties are susceptible, no cure for infected plants so they must be removed and destroyed as soon as possible. Remove weeds that act as host for onion thrips. 

chemical - onion thrips can be sprayed with dimethoate in cases of commercial crop or widespread infestations. 

In this example, I removed the affected plant and disposed of it in the rubbish bin - I didn't think my compost was reliably hot enough to destroy the virus. From what I have read, pesticides to control onion thrips have a very limited use in the home garden, although in commercial crops pesticides are best used to spray seed or cutting beds. 

references :  Judy McMaugh pg 189, 286

                      Kerruish E-13