Scientific Name Alternaria solani Identification Circular to angular spots with dark, concentric rings (target spots) develop on the older foliage Severe infections spread to younger leaves Lesions become quite large and are often associated with considerable leaf yellowing Fruit infections are not common, but may appear as a blackened area at the stem-end Often Confused With Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.) Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.) Period of Activity Early blight overwinters in infected crop residue. Spores are present throughout the growing season and may be carried long distances in the wind. Temperatures of 17- 24�C (63- 75�F) and extended leaf wetness favour early blight development. Scouting Notes Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. Thresholds Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Repeat sprays as necessary. Repeat at 5- 7 day intervals during continuous moist weather. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Applications should continue until close to harvest. Advanced Scientific Name Alternaria solani Identification The first signs of disease often appear deep in the canopy where the leaves stay wet. Lesions first appear on leaves as dark brown to black spots, 8- 13 mm (5/16- 1/2 in.) in size, on older foliage, but can grow much larger. Spots are circular to angular with dark concentric rings (target spot). The tissue surrounding the spot may be yellow. Lesions become quite large and are often associated with considerable leaf yellowing. If the disease is severe, lesions also appear on younger leaves. As lesions enlarge, their shape may become irregular. They are often bordered by leaf veins. Early blight may cause browning of leaf edges. Lesions may coalesce to form large dead areas on the leaf. Lesions may also appear on stems and blossoms (a cause of blossom drop). Fruit infection is uncommon, showing up as a blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit. Fruit symptoms are most common late in the season, especially when extended wet periods occur at harvest. Often Confused With Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.) Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.) Biology The fungus that causes early blight survive on decayed plant material in soil and can be seed borne. It is spread by wind. Period of Activity Early blight overwinters in infected crop residue. Spores are present throughout the growing season and may be carried long distances in the wind. Temperatures of 17- 24�C (63- 75�F) and extended leaf wetness favour early blight development. Unless the fungus is present on transplants, lesions generally don�t show up until flowering. Scouting Notes Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. Thresholds Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Repeat sprays as necessary. Repeat at 5- 7 day intervals during continuous moist weather. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Application should continue until close to harvest. Management Notes Reduce early blight inoculum by following a 3 to 4 year crop rotation. Ensure transplants are healthy and free of disease. Cultivars vary in tolerance to early blight. Overhead irrigation can promote foliar fungal disease due to longer periods of leaf wetness.

Avocados are not keen on chilly nights or hard sunlight. Or wind. If your day temps are higher than 80F and your plantlings have been living the soft life indoors they could have suffered sunburn. As a first move try some shelter - a burlap-covered frame like a tomato frame with one side open until they toughen up. You'll have some idea of whether it was a temperature problem when the plants start putting out new growth. Start with morning sun for a few weeks, give protection over noon, and allow some western light as they get older. You'll have to protect the trunks from heat - similar to citrus. It might also help if your usual fertiliser has some calcium in it as avocados appreciate a sweet soil. If there's no positive response then the next call could be to the local tree-crops advisor for information on local diseases.

Spider mites can't cause holes in the leaves, though they can cause discoloration and stunting... I'm guessing they aren't that severe yet, though. I'd love to have a better picture, if you can manage it, as I can't see what effect there is on the leaves. I will tell you that 1) nothing you did mulchwise or with the soil sounds bad, and 2) I don't know of anything soilborne that would cause quite this sort of effect. The sole exception is if some of that brush you burned was walnut trees... but even then, I'd expect wilting rather than streaking and stunting. Just based on the one picture, I'm leaning toward a virus (probably Potato virus Y or Tobacco etch potyvirus); the stunting alone screams either nutrient problems or virus, and I rarely see bad stunting from nutrient problems outside of hydroponic setups. Better pictures would help a lot in confirming or rejecting that theory, however. (dyannel or allisoncollins, feel free to contribute pictures too, if you have them.) --Alison

I think you'll find the answer posted in your duplicate post just a bit further down the page. Happy Gardening. Dave