Question
I live in southwest kansas. We have had an atypical wet spring summer and fall. My garden was infected with septoria leaf spot, started on my tomatoes and ran rampid through my garden. Got it identified by our local KU extension agent after it was too late. Also had powdery mildew on my squash and cucumbers. How can I kill out these fungi so they are not infecting my plants next season? Would it be safe to saturate the soil with the copper fungicide? Would that be effective enough? We have sandy soil, amended with peat moss and composted manure from a local livestock yard.
We have a big elm tree that sheds a black dust onto our vehicles and deck. Is it the culprit to our garden problem?
Thanks!

Answer
Septoria leaf spot is
best controlled using preventative measures. Destroy infested plants by burning or burying them.
Rotate vegetables to different parts of your garden each year to avoid areas where infested debris
(and thus spores of Septoria lycopersici) may be present. Use Septoria leaf spot-resistant tomato
varieties whenever possible. Increase spacing between plants to increase airflow and decrease
humidity and foliage drying time. DO NOT overmulch as this can lead to wet soils that can contribute
to increased humidity. Finally, where the disease has been a chronic problem, use of preventative
applications of a chlorothalonil-containing fungicide labeled for use on vegetables may be warranted.

Spraying the ground with a fungicide will not help. And the elm is not related to your problem. I would make sure you clean up ALL dead plant material from the garden now and  next year try to use resistant plants and do not mulch with plant material--these hold moisture and give the fungi a place to grow. If you feel the need to mulch I would suggest using plastic.
The black from the elm is more than likely residue from aphids--aphids secrete a juice called honeydew and a black mold grows on this.