An early symptom of bacterial
The lettuce is still safe to eat, though make sure to give it a good rinse. Those spots signal that cells have been weakened, making the lettuce a touch friendlier to any pathogens that happen to be nearby.
Downy mildew of lettuce is a disease caused by a fungus-like (Oomycete) organism, producing yellow patches and fuzzy white mould on leaves. These patches turn brown as the leaf tissue dies. It affects seedlings and mature plants.
Flea beetles (in the Chrysomelidae family) and darkling beetles (Tenebrionidae family) are common and can cause a lot of damage, not only to lettuce, but to a wide range of other plants in the garden as well.
Caterpillars attacking the fall crop are usually the most troublesome field pests of lettuce. In the greenhouse, aphid and cabbage looper infestations often give problems. Cutworms, whiteflies, leafminers, and slugs are slightly less important greenhouse pests.
Description of the Pest
Adult winged and wingless lettuce aphids have black markings on the joints of the legs and antennae. Some of the wingless aphids have many black markings on the top of the abdomen as well. The winged adults are browner than the wingless forms, but also have various black markings.
Washing leafy greens does not remove all germs. That's because germs can stick to the surface of leaves and even get inside them. If you eat contaminated leafy greens without cooking them first, such as in a salad or on a sandwich, you might get sick.
Look for irregular brown spots, mostly on the lower leaves, which contain large numbers of small black fruiting bodies of the fungus; these are characteristic of the disease. Look to see if the spots join together and the diseased areas become papery thin.
Tomato spotted wilt virus and Impatiens necrotic spot virus are closely related tospoviruses that cause indistinguishable symptoms in lettuce. Leaves of infected plants develop brown to dark brown spots and dead (necrotic) areas. Necrotic tissue can resemble burn damage caused by fertilizer or pesticide applications.
Tipburn is a feature of rapidly growing summer lettuce (but it can also occur in spring and autumn). It reflects the plant's inability to move enough water and nutrients to the rapidly growing leaf tissues enclosed in the heart of the lettuce plant.
Spots are evidence of pathogens or other microbes co-existing on the vegetable's surface, taking vital molecules as nutrients for their own survival. The good news is, these microbes are almost never bad for you. Though these microbes are bacteria, they are only pathogens that break down fruit – not humans!
The black spots come from decomposition of the plant related to breakdown by the fungus. Infection with bacteria can also cause a similar appearance. While kale leaves infected with a fungus or bacteria sounds ominous, it's not a problem for humans who eat the leaves.
Chemical. Maneb is a fungicide primarily used to manage downy mildew and is applied every seven to 10 days. Florida lettuce growers also use copper (hydroxide or sulfate) to manage downy mildew as well as bacterial diseases. Growers can also use sulfur to control several lettuce diseases.
Look for brown or black leaves that indicate rotting.
When the dark spots appear on multiple leaves in place of these colors, your lettuce is on its way out. Discolored lettuce often feels slimy and smells bad as well. Small brown spots usually aren't harmful if you eat them.
Decaying heads are at first slimy and brown but become dark brown to black as they collapse and dry. A webbed network of white to brown mycelium often grows over lesions, and small gray brown sclerotia later are apparent.
Overwatered lettuce plants will have wilted leaves that are soft and mushy to the touch. The leaves may also be yellow or brown in color and may start to fall off the plant. Another sign of overwatering is the presence of standing water around the base of the plant.
Treating Blight
Once blight is positively identified, act quickly to prevent it from spreading. Remove all affected leaves and burn them or place them in the garbage. Mulch around the base of the plant with straw, wood chips or other natural mulch to prevent fungal spores in the soil from splashing on the plant.
Bacterial leaf spot diseases often start as small dark brown to black spots with a halo of yellow tissue surrounding each spot. In some cases, the center of the leaf spot will dry up and fall out, giving the leaf a "shot hole" appearance.
Ali says to be on the lookout for black spots, slime, or an unpleasant odor. "Lettuce should be crisp and firm. If it snaps when you break or cut it, it's fresh and good to go—even if it has some red areas," Ali says. "If your lettuce has black spots, is slimy, or smells bad, it's past its prime and should be tossed."
Symptoms include diarrhoea, stomach cramps and occasionally fever. About half of people with the infection will have bloody diarrhoea. People usually notice symptoms 3 to 4 days after they have been infected.
The black spots or bugs you see on your onions, chives and garlic are black aphids which are merrily multiplying and sucking the life out of your plants. Some appear bigger than others – these are the 'mothers', which have wings. These aphids do not produce eggs but leave hungry young straight on to your plants.
You can often control aphids by wiping or spraying the leaves of the plant with a mild solution of water and a few drops of dish soap. Soapy water should be reapplied every 2-3 days for 2 weeks.
You can wash them off, but it may take a bit of extra time. They don't come off with a simple rinse in water because they adhere to the surface of the plants. So you have to swish them around in cold water that has a pinch of salt (or a drop of soap) in it.
Improves Nutrient Uptake
Epsom salt contains magnesium, which is an essential nutrient that helps a plant perform some of its essential functions. One of these is that magnesium increases a plant's ability to absorb other nutrients, such as nitrogen and phosphorus, without which it would struggle to thrive.