Lentil

A small beetle (Acanthoscelides) whose larvae develop inside stored dry beans, hollowing the seed and boring round exit holes - the classic ruin of a jar of home-grown beans. Eggs are often already in the pod at harvest.

Watch for: Round holes in stored beans, fine powdery dust in the jar, tiny beetles emerging, and hollowed or tunneled seeds.

Prevent: Harvest and dry promptly; store fully dried beans airtight; and above all, freeze shelled beans for at least a week before storing to kill any eggs and larvae.

Treat: Freeze or heat-treat infested lots to kill the weevils; discard heavily damaged beans; keep new stores away from old to prevent reinfestation.

On lentils the culprit is usually a related bruchid (Bruchus lentis) rather than the bean weevil itself, but the story and the fix are identical: eggs ride home from the field inside the seed, so freeze the cleaned lentils for a week before they go into a jar.

A fungal blight of cool-season pulses - lentil, chickpea, pea and faba bean each have their own closely related Ascochyta species - that spreads in cool wet weather by rain splash and infected crop debris. Tan-to-grey lesions with dark margins appear on leaves, then girdle stems and sink into pods, and the fungus grows through the pod wall into the seed itself. That is what makes it serious for anyone saving their own seed: the disease overwinters inside the seed and in last year's straw, so one wet season can carry into every planting that follows. Severe infections defoliate plants, shrivel the seed, and stain the crop.

Watch for: Round to irregular tan or ash-grey spots with distinct dark brown margins on leaves, often peppered with tiny black specks in the centre. Dark sunken lesions girdling stems, so whole shoots wilt and die above the point of attack. Sunken discoloured blotches on the pods, and stained, shrivelled, or pitted seed when you shell them. Damage worst after a cool wet spell, heaviest low in a dense canopy, and often spreading outward in patches from one starting point.

Prevent: Start with clean, certified seed rather than saved seed from a stand that showed any blotching - this is the single most effective step, because the fungus travels inside the seed. Rotate at least three years out of the same pulse, and do not plant next to last year's stubble, since spores blow and splash off old straw. Sow into well-drained ground at a sensible density so air moves through the canopy, and do not work among wet plants. Where resistant varieties exist for the pulse you are growing, use them.

Treat: There is no cure for infected tissue. Pull and bin badly affected plants rather than composting them, keep off the stand while it is wet, and harvest what is sound. Above all, do not save seed from an infected crop - buy fresh clean seed and start the line again. Protectant fungicides are used commercially at early bloom, but for a home planting rotation, clean seed, and airflow are what actually decide the outcome.

The disease most likely to end a home lentil crop in a wet spring, and the reason to buy fresh seed after a blotchy year rather than replanting your own.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Watch for: Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Prevent: Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Treat: Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

The pea aphid is the species that matters here - a big green aphid that works the growing tips and flower stalks of lentils, peas and vetch and can carry pea enation mosaic and bean leafroll viruses into the stand. The feeding itself is rarely worth treating on a vigorous planting.

Root rot is not one organism but a group of soil fungi and water molds - Pythium, Phytophthora, Fusarium, Rhizoctonia and others - that sit harmlessly in most soils and only turn destructive when the ground stays saturated. Waterlogged soil drives the air out, the roots suffocate, and the weakened tissue is invaded and goes soft, brown, and stringy. Because the damage is underground you usually see it first as something that looks like drought: wilting, yellowing, stunting, a plant that does not respond to being watered. Overwatering, heavy compacted ground, a low spot that collects runoff, a pot with no drainage or a saucer left standing full, and cold wet soil in winter are the usual causes. Once roots have actually rotted there is no cure - this is a problem you prevent rather than treat.

Watch for: Wilting in the middle of the day on a plant whose soil is damp - the classic tell, and the reason people water a rotting plant and finish it off. Leaves yellowing from the bottom up, dull off-color foliage, and growth that stalls for no visible reason. Whole shoots, or one side of the plant, collapsing while the rest still looks fine. Soft, dark, or mushy tissue at the base of the stem or at the crown, sometimes with a sour smell. Lift a failing plant and look at the roots: healthy ones are firm and pale, rotted ones are brown or black and slimy, and the outer layer slips off between your fingers leaving a thread of core behind. Seedlings that topple over at soil level are the same problem, called damping-off.

Prevent: Drainage is the whole defense. Match the plant to the site first - something that wants sharp drainage will not survive heavy clay or a low, water-collecting spot however well you tend it. Where the ground is heavy, plant on a raised bed, berm, or slope, or grow in a container. Set plants at the depth they were already growing, since burying the crown or the root flare is a common cause of rot, and keep mulch pulled back a few inches from the stem base instead of piled against it. Water the soil rather than the calendar: check that the top inch or two is dry before watering again, cut back hard in cool weather and winter dormancy, and never leave a pot standing in a full saucer. Do not plant or dig in soggy ground, and go easy on rich amendments for plants that want it lean. Rotate annual crops, and start with clean healthy plants and fresh mix.

Treat: There is no cure for tissue that has already rotted, so act on the conditions rather than looking for a spray. Stop watering at once and fix the drainage - open up compacted soil, or move the plant to a raised, sharply drained position or a container. Lift a badly affected plant, cut away every soft dark root and rotted section with a clean blade back to firm pale tissue, and replant only the healthy parts into fresh free-draining soil or mix. Often the better move is to give up on the plant and save its offspring instead: cuttings, offsets, or divisions taken from firm healthy growth root readily and give you a clean start. Bin the rotted material rather than composting it, and correct the drainage before you replant, because the rot comes straight back in the same wet spot.

Lentils are sown into cold spring ground and are unusually intolerant of wet feet, so this is the commonest cause of a thin or patchy stand. Sow into raised, sharply drained beds, resist watering cold soil, and rotate away from peas and vetch.

Powdery mildew is a fungal disease that coats leaves - and often stems, buds, and fruit - in a white-to-gray powder that looks like spilled talcum. It is not one fungus but a large family of them, each fairly specialised to its own group of plants, which is why mildew on one crop rarely jumps to an unrelated one beside it. Unlike most leaf diseases it does not need wet leaves: it thrives on warm dry days followed by humid nights, and it takes hold fastest where plants stand crowded in still air or in shade. The coating blocks light, so heavily covered leaves yellow, brown, and drop early. On many plants that is mostly disfiguring and arrives late enough not to matter; where it strips away the leaves a crop still needed to finish, it costs you size, sweetness, and quality.

Watch for: Round white powdery spots on the upper leaf surfaces that spread and merge until whole leaves look dusted. It usually starts on the oldest, lowest, most shaded leaves and works upward, so check there first. Look at the undersides too, and at stems, buds, and flower stalks, which get coated as it advances. Leaves that yellow, brown, curl, or go crisp and drop early under the coating. New growth that opens small, crumpled, or twisted where the fungus has reached the shoot tips. On plants where it gets onto the fruit, a dull gray film, russeted or scarred skin, and cracking. Late in the season, tiny dark specks scattered through the white felt - that is the fungus setting up to overwinter on the debris.

Prevent: Give plants room. Crowding and still air are the biggest single driver, so space at the full recommended distance, thin seedlings properly, and divide or prune out congested growth until air moves through the plant. Full sun and an open position help; deep shade and a still corner against a wall are where it always starts. Water at the base rather than overhead, and water early in the day so nothing stays damp overnight. Keep plants evenly watered - drought stress at the roots leaves them far more susceptible, even though the fungus itself likes dry air. Go easy on nitrogen, since soft lush growth is the most vulnerable. Where resistant varieties exist for what you are growing, choosing one is the single most effective thing you can do on a plant that mildews every year. Clear infected leaves and stems away at the end of the season rather than composting them.

Treat: Start early: sprays protect healthy tissue, they do not clean up leaves that are already coated. Pick off and bin the worst leaves as soon as you see them, and open the plant up by thinning or pruning so air moves through. On anything that regrows quickly, shearing the whole plant back forces a clean flush and beats spraying. If it keeps spreading, potassium bicarbonate, horticultural oil, or neem applied weekly will hold it - cover both leaf surfaces. Sulfur also works, but it burns the foliage of some plants, should never go on in heat, and must not be mixed with or applied close behind an oil spray. Whatever you use must be labeled for the plant you are treating: follow that label and observe its pre-harvest interval on anything you eat. Do not compost badly infected material. Late-season mildew on a plant that is finishing anyway is usually cosmetic; on a crop still filling out it is worth acting on.

Usually arrives on lentils only at the very end of the season, once the pods have filled and the plants are drying down anyway - in which case it is cosmetic and needs nothing. A thickly sown, unstaked stand in still air is where it turns up first.