Blossom End Rot is a physiological disorder which looks like rot on the side of the fruit opposite the stem and is associated with low concentrations of Calcium in the fruit. Rot is induced in life stages such as fruit ripening when the demand for Calcium for the fruit walls is high enough to exceed supply. It can also be induced by high levels of competing cations, drought stress, and excessive soil moisture fluctuations - all of which affect the uptake of Calcium ions. Additionally, over fertilization that causes rapid growth can cause blossom end rot because the plant won't have enough time to uptake Calcium as the fruit is developing so quickly.
This rot can be managed by maintaining the soil around 6.5. Liming to do this both supplies dissolved calcium ions and reduces the levels of competing cations. Using nitrate as a Nitrogen source as opposed to ammonia which reduces Calcium uptake. It is also important to avoid over-fertilization during fruiting. To avoid drought stress and fluctuations in soil moisture, mulch and consistent irrigation should be used.
EARLY BLIGHT:
Early Blight is a fungal pathogen spread when alternaria spores land on a leaf surface. The spores then germinate and penetrate the leaf tissue. The fungal mycelia grow and expand to produce a characteristic brown, circular lesion on the infected tissue with dark concentric rings. The spores can be spread by the wind, contaminated tools, and running water and their germination is encouraged on wet leaf surfaces and in temperatures between 65 and 85 degrees Fahrenheit. Tomatoes are most susceptible when their fruit is aging because this is when nutrient demands are highest and therefore nutrient concentrations in tissue where the spores can grow are highest. The fungus generally moves up the plant to the younger leaves.
Management recommendations include a three year or greater crop rotation, removing all potentially infected crop debris and plants as soon as they're discovered, and avoid standing water on leaves and fruit (especially during fruit maturation)
SOUTHERN STEM BLIGHT:
Southern Stem Blight is a fungal pathogen which results in wilting and eventual plant death in infected plants. Sun scald can occur as a result of the wilting or dead foliage. Plant death is accompanied by a characteristic white ring of cottony mold at the soil line punctuated by brown spots (sclerotia) which develop in late stages of infection. Infection patterns begin with a single plant or hot spot and move outward to infect nearby plants creating infection zones in the field.
The blight can be avoided by staying away from fields with a history of disease and immediately removing roots and stem debris when discovered. Incorporate covers early to ensure that the debris has rotted well before transplanting tomatoes and peppers. Good weed and grass control through cultivation, mulching, etc. will also help to avoid fungi living in debris.
PHYTOPHTHORA CROWN:
Phytophthoro crown is a soil born pathogen that primarily attacks seedlings of peppers, tomatoes, and eggplants. When the soil is saturates, phytophthora produces zoospores which can travel through water filled pores to infect the plant tissue. It can also produce chlamydospores and oospores which can survive up to three years in the soil. The infection generally occurs in cool to moderate temperatures and causes brown discoloration in plant tissue. Specifically, it initially causes stunting and small leaves but plant collapse occurs later. When the dead plant tissue is cut open, brown discoloration in the crown vascular tissue can be seen. The same species can also attack roots causing brown or black rot.
It can be managed by controlling water flow strictly in the field. Raised beds reduce the amount of standing water as does preparing the beds carefully for good drainage. It is imperative to buy resistant cultivars if there is a history of phytophthora in the field but buying certified transplants or seed is important no matter what. Drip irrigation should be used and monitored carefully to avoid standing water on the leaves. Also, runoff water should not be used on or near other plants. To avoid runoff water which might inadvertently reach your solanaceous plants, make sure to account for slope in your crop rotation.
VERTICILIUM WILT:
Verticilium is a wilt that affects tomatoes, peppers, eggplant and tomato equally and can live in the soil and in weeds as alternate hosts for years. The symptoms may be confused with Alternaria/ early blight but the spots are less definite and have no concentric rings. Specifically, verticilium wilt causes yellow blotches on the lower leaves until brown veins appear followed by chocolate brown spots immediately prior to plant death.
A 4-5 year rotation is necessary to manage verticilium wilt if it shows up in a field. Well-drained soils and raised beds also prevent transmission and, in general, soil moisture should be kept as a minmum to avoid transfer within the soil water. If verticilium has been a serious issue in the past, the soil can be solarized prior to planting to control the populations of the pathogen.
FUSARIUM WILT:
Fusarium wilt is often confused with verticilium wilt in its early and has similar causative agents which mean that is is managed in the same way. However, in later wilt stages, fusarium can cause cankers and brown streaks. Also, fusarium doesn't affect the whole plant uniformly. Symptoms also vary by species. See the attached table for details on how the symptoms present in each plant. See the above section on verticilium wilt for management strategies.
BACTERIAL SPOT & SPECK:
Bacterial spot and speck are both bacterial pathogens introduced to a field by contaminated seed or transplants and spread by splashing rain or by equipment during cultivation. Outbreaks are favored by excessive overhead irrigation, frequent warm, driving rains, and long dew periods. The only differences between the two are the size of the necrotic spots and the optimal temperatures under which they flourish. Bacterial spot is common in soil temperatures of 75 to 85 degree weather while speck is favored in 65 to 75 degree temperatures.
Bacterial infections can be managed by ensuring that you buy certified seeds or transplants as well as buying resistant varieties if you have had issues historically or in nearby fields. Having a minimum of three year rotation can control the bacterial community. Avoiding excessive Nitrogen fertilization in which the bacteria can breed is important. Avoiding irrigation or handling the plants while they're wet also helps to avoid spread in your fields. Remove field debris as soon as speck or spot is observed but it's not imperative to remove the infected plant immediately unless runoff will touch the fruit and infect other plants downslope.
ROOT KNOT NEMATODES:
Root knot nematodes are microscopic roundworms that live in the soil and attack the roots of young plants. The nematodes reduce the root volume which, in turn, affects the nutrient and water absorption capacity of the plant. The optimal soil temperature for nematode population growth is 70 to 80 degrees Fahrenheit.
To manage nematode populations, it is important first to determine the nematode density prior to planting by sending a soil sample to a nearby extension agent. Cover crop between planting with hairy indigo, American jointvetch, or sorghum. The field can also be fallowed for a year to starve the nematodes if the cover crop will not establish quickly enough to smother all other nematode hosts (including weeds). Mulching with organic matter that has balanced microbial populations can also be beneficial because these populations can outcompete the root knot nematodes. Soil solarization can decrease the nematode populations. Resistant cultivars exist.
COMMON SCAB:
Common scab is a tuber disease that affect potatoes exclusively in the solanaceous family. It impacts marketability but not necessarily the yield of potatoes. Different types of scab can present, though all including circles of corky or scabbed tissue on the tubers and are caused by the same species of bacteria. The type of scab is determined by the host resistance, the aggressiveness of the infection, the strain of both bacteria and plant, etc.
The bacteria populations which cause common scab will always be present in fields but the populations can be suppressed at highly acidic pHs (below 5.2). Rotations with non-hosts (such as small grains, corn, or alfalfa directly after a potato crop) also reduces populations. Planting radishes, beets, carrots, or crimson clover prior to potato crops encourages growth in the bacterial populations. Consistent soil moisture should be provided to avoid scab during the 2-6 weeks following tuber initiation because the bacteria in the water outcompete the scab. Thick applications of alkaline producing organic matter should also be avoided.
TOMATO SPOTTED WILT VIRUS:
Tomatos Spotted Wilt Virus is a virus transmitted by thrips that affects a wide variety of plant species. In the South, it generally only presents in greenhouses. Symptoms differ by plant species but generally include yellowing and/or necrotic spots on leaf tissue as well as characteristic necrotic rings on fruit.
TSWV can be managed by testing for thrips in the greenhouse regularly and throwing out or submerging transplants when discovered to get rid of them. Also avoid mowing weeds or cover that might be alternate hosts for thrips while the transplants in the greenhouse are being aired. Stock the greenhouse with yellow sticky traps. Blue traps catch more thrips but the yellow ones are more universal.
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