Late blight, which is caused by a fungus Phytophthora infestans, is one of the most destructive and contagious plant diseases directly affecting the fruit and killing the plant. (Phytophthora means ‘plant destroyer’ in Latin)
Late blight spreads like a wildfire. This fungus produces spores in abundance and with the help of moist wind they will travel up to 30 miles. It is imperative to destroy infected plants as soon as possible as this disease is easily spread.
This disease shows up in late summer as the hot and warm humid days may be followed by cool and moist nights with accompanying rain, fog and heavy dew. This is a indicator to the home gardener to become watchful for the signs of late blight.
What to look for:
- Leaves will develop water soaked spots.
- The spots will enlarge and quickly turn from brown to purple to black.
- Shoots of the plant will turn black and eventually the plant will collapse.
- As the plant rots there is a foul odor; a whitish mold may be present.
- Tomatoes will show grayish water soaked spots, enlarge and turn dark. They may have additional rot, an unpleasant foul odor and be mushy.
- Potato tubers will show purplish or brown corky spots. There may be additional rot, an unpleasant foul odor and be mushy.
Can this disease be prevented?
- Check your potatoes and tomatoes daily following cool, humid and prolonged wet weather followed by warm/hot humid days. Sign up to receive alerts (www.usablight.org) for immediate notification when late blight is confirmed near you.
- Copper fungicides (Elemental copper as cupric oxide) can be highly effective if applied as a preventative (before infection) and with complete coverage of all plant foliar surfaces, including the undersides of leaves where the fungus typically produces spores. Follow the label and use as prescribed.
- Neem oil is an alternative fungicide. Follow the label and use as prescribed.
- If symptoms are found remove the plant(s) immediately in plastic sealed bags.
- Remove the plant(s) when the leaves have dried to decrease the dispersal of spores.
- Dispose of this diseased material in plastic sealed bags with your household trash. Burning the diseased plant material is equally effective.
- Change your clothing and wash your hands/change your gloves before entering the garden again. (Spores from late blight could be reintroduced from your clothes, hands and gloves) Remember this is a highly contagious disease.
- Hill your potato plants to stop spores from draining down to the tubers.
- Some gardeners will cover their tomatoes with an old tent frame or swing set and place plastic over the frame. The frame must be higher than the planting and permit air movement as there cannot be condensation on the leaves. High tunnels have been very successful.
Are there blight resistant tomatoes?
An article in growveg.com (January 17, 2014) by Barbara Pleasant offers a list of 9 blight resistant tomato varieties offering excellent to very good resistance.
- Defiant PHR
- Lemon Drop
- Matt’s Wild Cherry
- Mountain Magic
- Mountain Merit
- Plum Regal
- Mr. Stripey (AKA Tigerella)
- Iron Lady
Are there blight resistant potatoes?
- Elba, most resistant
- Jacqueline Lee
- Island Sunshine
- If there are symptoms as harvest approaches remove all potato foliage from the garden and wait 2 weeks before digging the tubers.
- Wait for dry conditions to dig your potatoes.
- Remove all potatoes from the soil. ( the spores of this fungus will overwinter in unharvested tubers, in the soil and living crop debris)
- Check your harvested potatoes for spots and cull if spots are present. Do not store spotted (culled) potatoes with unaffected potatoes.
- Any fruit that rot after picking should be put in a trash bag and disposed with household garbage.
- Unaffected parts of fruit can be consumed, but fruit from affected plants should not be canned due to concern that the pH may not be sufficiently low.
- Tomato seed is not a carrier of this disease.
A photo gallery of this disease: http://www.hort.cornell.edu/lateblight
Cleaning the garden of all living debris, tomatoes and potatoes is essential. Burn or bag this debris for disposal. Do not compost. Again, this is a very contagious disease.
Is there a cure?
Late blight has been with us a long time. The potato famine in Ireland of 1845 was caused by late blight. As you have read this disease is highly contagious and your daily observations are necessary to spot the symptoms and act accordingly.
Russeting is characterized by multiple micro cracks in the tomato skin which are often concentric; also called cuticle cracking. This disorder is caused by fluctuations of soil temperature and soil moisture.
This is a physiological disorder – a problem caused by the growing conditions rather than by a pest or disease agent. Inappropriate levels of water ( drought, fluctuations in watering/rain, flooding), light, temperature (stop and start growing) and nutrients can all cause a variety of physiological disorders in tomatoes.
The fruits are especially vulnerable as they are at the growing tips and have to compete with the new shoots for water and nutrients.
The cuticle, the very outside, transparent layer, of the fruiting skin may become less elastic. As the fruit grow, the cells of the fruiting skin loose their elasticity and small cracks start to appear.
Excessive temperature changes during the daytime and nighttime cause the skin of the fruit to react to the air around it. Water condensation within the skin of the fruit may expand and contract causing cracking.
These suggestions may remediate tomato russeting:
- Apply adequate mulch in hot weather to keep the soil cool and decrease evaporation.
- Consider raised bed gardening for better drainage.
- Water in mid-morning.
- Use shading material to enhance a cooling effect on the entire.
- Pick tomato early when fruit shows color.
I just uploaded a new video documenting how to make and install floating row covers.
Supplies you will need:
- Rebar – 3/8″ x 10′, cut into 5 – 2′ lengths
- Electrical PVC – 1/2″ diameter pipe x 9′
- Floating Row Cover fabric
- Angle Cutter or equivalent for cutting lengths of rebar
- Hack Saw or PVC Pipe Cutter
- Gloves and Safety Glasses
Low tunnels using floating row covers is of great benefit for several reasons.
- Floating row cover is a light weight, breathable fabric that allows air, moisture and sunlight to pass through the material.
- There are various fabric weights to meet different needs.
- Agribon 15 is lightweight fabric that is used for insect protection and shading.
- Agribon 50 is a heavy cloth used for freeze and frost protection. This cloth will protect a crop down to 26° (F)
- Insect protection – when properly sealed, insects cannot penetrate the covering which protects the crop from damage and disease.
- Problem insects such as Japanese beetle, squash bugs, squash vine borer, cucumber beetles and flea beetles are blocked from doing their usual mayhem.
- Isolation chambers – Low tunnels are ideal for seed saving of crops such as squash, pumpkin, melons and watermelons. Bumble bee hives may be inserted at one end of the enclosure to insure proper pollination. Plus, there is not a chance of cross pollination. You may grow several varieties side by side. That is a huge advantage.
- Season extension – row covers placed over a crop will allow for early planting by trapping 2° – 8° (F) higher temperature. Likewise using a row cover late in the season will protect the crop from early frost. By using this method you can easily extend your growing season by one month!!!!
- Hoop houses, high tunnels and greenhouses – row cover gives added protection and benefits the grower with lower fuel costs. The insulatory value of the row cover will block some of radiant cold that may damage a crop.
This is another method and tool for your gardening arsenal!!!
I’ve grown broccoli for the last two years and all I get are huge plants with either little or no flower heads. What seems to be the problem?
Timing is key!! Broccoli likes to stay cool.
Causes of no or poor flower heading:
- Alternating periods of abnormal high temperatures followed by abnormal low temperatures stresses the plant and causes heading to come to a complete halt.
- Stress brought on by drought or inadequate moisture.
- Excessive nitrogen can cause huge healthy plants with little or no head production.
- Transplanting too late with root bound plants will keep the broccoli from heading.
- Transplants when exposed to temperature of 40 degrees and below for 1 – 2 weeks triggers heads to form too early or not at all.
- Transplants not properly hardened off will be stressed and perform poorly. https://papasgardens.com/2015/04/24/what-does-it-mean-to-harden-off-seedlings/
- Overcrowding results in either little or no head formation due to competition for adequate water and nutrient.
- Proper timing of transplanting for your specific area. Your County Cooperative Extension Service will supply the dates for planting.
- Proper planting of transplants 2 feet apart.
- Even supply of moisture. Drip irrigation is best.
- Balanced nutrition/fertilization. Avoid excessive applications of nitrogen.
- Proper hardening off of transplants.
- Cover planting when temperatures drop below 50 degrees. Low tunnels with floating row cover or cloches will provide protection.
- Plant in Fall.
- Decreased pest pressure.
- Plants are usually stronger. The flower heads are bigger.
- Plants grow better into cooler weather.
- Sow seeds for transplants 10 – 12 weeks before first frost.
- Set transplants 2 feet apart for extended season planting.
Broccoli are sensitive to their environment. When treated with care, they will reward you!