The last week has proven a large infiltration of these disease causing pathogens of Fusarium/Verticillium, Bacterial Spot and Speck, and Septoria Leaf Spot. As I talked about previously on water, some of these can be worse than others and spread much easily. When it comes to diagnosing what you have, it can sometimes be quite complicated. Many of these look the same with early and late symptoms that are very similar. At the same time, it's possible for one to lead to another. One pathogen attacks the plant early leading to plant damage that allows for another pathogen to move in. But for the sake of today's blog post, let's just look at each one on it's on.
Bacterial Spot or Speck
Both bacterial spot and speck will target leaf tissue and also hit tomato fruit. These are sometimes talked about equally as symptoms can look very similar and both can be on the same plant. Bacterial speck though is primarily transferred by seed. If you purchased plants and small lesions are on them, chances are that is it Bacterial Spot. Lesions appear on leaf tissue surrounded by what we call a yellow halo seen in the picture below. Solutions then are to rotate out of peppers/tomatoes for at least 2 years, remove tissue from being incorporated into the soil, and not be gardening under wet conditions if you can help it.
This wilt cause browning/yellowing of leaves with wilt conditions. The only way to distinguish between these two is in the laboratory. Fusarium typically likes warm weather while Verticillium favors cold weather. Both are soil-borne pathogens where they enter the roots first. They also typically enter the field by way of infected plants or seeds. One of the tools that I use in the field is to take an infected stem and split down the middle like below. If browning is occurring, this is typically a sign that you have this wilt. Control methods include rotating out of tomatoes/peppers for the next 5-7 years, choosing varieties that are resistant to these diseases, and removing/destroying debris.
Source: Univ of Minnesota Extension
Septoria Leaf Spot
This spot is noticeable by the small, circular leaf spots on lower leaf tissues. Leaf tissue may also drop prematurely. This is one that I've yet to see this season and can sometimes be misdiagnosed. As you'll see in this photo, it can eventually evolve into very blackish/brownish leaf tissue which can sometimes be a give away. It may also look similar to Spot/Speck. Control methods are similar to others with crop rotation, remove debris after the season, spacing plants properly to allow for air circulation, irrigate in the morning, and remove leaves at first sign of damage.
Hopefully this has provided you with a good overview of these. I'm also available to diagnosis any of these that you might be seeing along with our Master Gardener Helpline within your county (Hours vary and can be found on our homepage). I'll cover Late/Early Blights very soon as these are the next diseases we'll be dealing with.