Tomato troubleshooting
“In all my years growing tomatoes, I’ve never seen a worse year,” gardeners tell me every so often. I hope this isn’t your worst year. Either way, there are reasons why it’s been tough. Disease or pest issues can be tricky to figure out, so this week I’ll cover major fungus and bacterial diseases that affect tomatoes.
We know weather makes a huge difference with crop successes and challenges. Many gardeners had phenomenal early season vegetables — broccoli, lettuce, spinach and other leafies loved the cool, wet spring. We didn’t buy lettuce from May to July, just enjoyed home-grown.
Many tomatoes were planted over Mother’s day weekend, which was followed by six days with nighttime temperatures in the 30s. The lowest was May 12 at 30 degrees. June wasn’t much warmer — nine days in the 40s. Tomatoes are very cold-sensitive and will just sit when nights are in the low 50s. Once it warms up, they need to play catch-up — and some plants never do.
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Then it rained and rained some more, with hail followed by hail. Some gardeners got it, some didn’t. And some survivors had it worse than others. Extreme heat last week, monsoons and tornadoes this week!
Many tomato and other plants are unhappy and showing it. Check your plants for the following common ailments. To get a confirmed diagnosis, take a few sick leaves or a close-up photo to your local garden center or Colorado Master Gardener county office.
Early Blight is caused by the fungus Alternaria solani. It can also affect potatoes, peppers and eggplant. Spores overwinter on host weeds and plant debris, and then are blown or splashed onto lower leaves. They easily spread to adjacent leaves and other plants during warm, wet weather. Tomatoes are more susceptible to infection when they begin to set fruit; blight is most noticeable during hotter months. One-half-inch, brown to black, target-like spots, surrounded by a yellow border develop on lower leaves first, then progress upward. Leaves eventually turn brown before dropping. Severely infected plants will produce low yields of undersized fruits (they are, however, edible).
Cultural controls help to prevent early blight and other tomato issues. Never work around wet plants. Slow early blight by removing infected leaves along with their stems (I sterilize my shears between cuts on all diseased plants). Mulch around each plant to prevent water from splashing up and leaves from touching the ground. And always water at the base of the plant, never overhead. If this is unpreventable, water early in the day so that leaves dry quickly. Low nitrogen levels favor early blight, so a mid-season application may be helpful when tomatoes reach 2 inches in diameter. Remove all leaf tissue at the end of the season and don’t compost it. Do not plant tomatoes in the same place each year if possible — and don’t crowd them.
There are several types of chemical and organic fungicides on the garden shelf. Read each label carefully about application times and precautions to avoid harming aquatic life, bees and beneficial insects. Organic products such as potassium bicarbonate and Bacillus subtilis are effective when used before early blight hits, or at the earliest onset, then at 7- to 10-day intervals.
Septoria leaf spot is caused by a different fungus, Septoria lycospersici. Like early blight, it can also affect potatoes, peppers and eggplant. And guess what: tomato plants can have early blight and septoria leaf spot at the same time. Same deal: the fungus overwinters on crop and weed foliage. This is why it is so important to remove diseased leaves. The spores easily spread during cool wet periods. Small, numerous light spots with dark margins appear on lower leaves. Later, black dots appear within the spots. Affected leaves eventually wither and die, and the fungus spreads upward. Controls are similar to early blight; just make sure sprays include septoria on the label. Compare the two diseases at learningstore.uwex.edu/assets/pdfs/A2606.pdf
Bacterial Speck and Bacterial Spot diseases aren’t often seen in our area, but are showing up now because of high moisture. Spread by wound entry (think hail and heavy wind hitting your plants), speck symptoms can appear on any plant part. Leaves are covered by small, dark brown, irregular patches with yellow halos that often tear. The patches turn black and can appear blistered. Spot symptoms are similar to speck, but the lesions seem more greasy in appearance. On the fruit, speck lesions are sunken; with spot, they’re raised and scabby on spot.
To control it, do pretty much the same things: always water at the base of plants and clean up all plant debris each fall. Do not save seed from infected plants. This disease survives in the soil for a year, so rotate tomatoes and other nightshades (peppers, eggplant, potatoes) and other plant families. Use disease-free seeds and transplants next year.
Copper sprays provide some control of speck and spot before flower and fruit set. The fruit is edible; just peel away the scabs.
More on recognizing tomato problems: www.ext.colostate.edu.
In the Landscape
Early August is a good time to sharpen blades and tune lawnmowers for the remainder of the season.
Grass will grow quickly after the recent rains. Mow high, mow often and let the clippings remain to add nutrients to your lawn.
Replant quick-maturing crops like lettuce, kale, Asian greens, spinach, radishes, turnips, Swiss chard and beets.
Sneak in one more sowing of basil seeds in some open soil or containers. Grow enough to harvest in September and process to freeze for winter use.
PEST WATCH: SPOTTED WING DROSOPHILIA
This small fruit fly of East Asian origin has arrived in our area. It attacks soft fruits including raspberries, blackberries, grapes, plums, peaches and cherries. Unlike indoor fruit flies that prefer overripe fruit, the spotted wing drosophila female lays her eggs in undamaged fruit. The larvae develop as the fruit ripens, which greatly affects fruit quality (and your ick factor when you find them). Remove damaged fruit, toss it in a close container and do not compost. More: wci.colostate.edu/shtml/SpottedWing Drosophila.shtml
Betty Cahill http://gardenpunchlist.blogspot.com/
