Gadenin日本語Get the appThe early threats: mice, slugs and birds
Most sweet peas that are lost are lost before they are a foot tall. Mice dig sown seed out of pots and trays, particularly in a cold frame over winter where the food is easy and sheltered, and they can empty a whole batch in a night, leaving small holes and scattered compost. Cover newly sown pots with fine mesh or a sheet of glass until the shoots are through.
Slugs and snails take the seedlings after that. A young sweet pea is soft, low to the ground and highly attractive on a damp spring night, and one grazed off at the base does not regrow. Protection has to go down on planting day, not when you notice the damage, because by then the plants are gone. Check in the evening with a torch for a few nights after planting to see what you are dealing with.
Birds pull at soft young shoots, especially in early spring when other greenery is scarce. This is intermittent and rarely fatal, but a row that keeps losing its growing tips will never make a decent plant. Netting or a few short canes with string over the young row is enough to stop it.
All three of these become irrelevant once the plants are climbing. If a row makes it to two feet (60 cm) intact, the early pests are behind you and the remaining problems are aphids, weather and mildew.
| Problem | What you see | What to do |
|---|---|---|
| Mice | Sown seed dug out of pots, neat holes, no seedlings | Cover pots with mesh or glass until shoots emerge; trap in the frame |
| Slugs and snails | Young plants grazed off at the base overnight | Protect from planting day; check at night with a torch |
| Birds | Soft growing tips pulled off young plants | Net the row or run string over short canes until it is climbing |
| Aphids | Clusters on growing tips and flower stems, sticky leaves | Jet of water, squash by hand, encourage predators; act early |
| Pollen beetles | Small shiny black beetles inside open flowers | Harmless to the plant; leave cut stems in a dark shed for an hour |
| Powdery mildew | Gray white dusting on leaves late in the season | Water at the base, thin crowded growth, remove the worst leaves |
| Virus | Mottled or streaked leaves, distorted stunted growth | Pull and dispose of the plant; control aphids on the rest |
| Root rot | Plants wilting despite wet soil, blackened stem base | No cure; improve drainage and do not replant in the same ground |
Aphids matter more than the damage they do
Aphids cluster on the growing tips and the flower stems from late spring onward, and in themselves they are a minor nuisance: they distort a few new leaves, leave sticky honeydew that goes sooty black, and are easily knocked off with a jet of water or squashed between finger and thumb. A healthy plant shrugs off a modest infestation.
The reason to take them seriously is virus. Aphids move between plants carrying viruses that stunt sweet peas badly, giving mottled or streaked leaves, distorted growth and flowers that are marked or malformed. There is no treatment. A plant showing that pattern should be pulled out and disposed of, not composted, and the aphids on the rest of the row dealt with before they spread it further.
Deal with aphids while there are a dozen of them rather than a thousand. Check the growing tips every time you pick, which you should be doing every two or three days anyway, and rub out the first colonies by hand. Ladybirds, hoverfly larvae and parasitic wasps arrive within a couple of weeks if you do not spray broadly, and they hold the population down for the rest of the season.
Avoid a general insecticide on a plant this heavily visited by bees. Sweet peas are worked constantly by pollinators, and spraying the flowers costs more than the aphids do. If you must intervene beyond water and fingers, use a soap based product in the evening on the affected tips only.
- Inspect the tips on every picking round Turn over the top two or three leaves and look at the flower stalks. Aphid colonies start small and in one place. Thirty seconds of looking, twice a week, prevents nearly every serious infestation.
- Use water and fingers first A firm jet from a hose knocks most of a colony off, and they do not climb back. Squash what remains between finger and thumb. Repeat in three days; one pass never gets all of them.
- Pull any plant with mottled distorted growth Virus does not recover and the plant is a reservoir for the rest of the row. Take the whole plant out, roots and all, and put it in the rubbish rather than the compost pile.
- Leave the pollen beetles alone The small black beetles found inside the flowers do no real harm. If they spoil cut flowers, stand the stems in a bucket in a dark shed with one light source nearby for an hour and most will leave on their own.
Powdery mildew at the end of the season
Powdery mildew is the disease that closes the sweet pea year. It appears as a gray white dust on the upper surface of the leaves, usually starting on the crowded lower growth in the second half of the season, and spreads upward until the foliage is gray and the plant is visibly finished. It arrives in warm dry weather when the roots are dry, which is exactly the same weather that ends the flowering anyway.
Because it comes at the end, it is rarely worth spraying. What is worth doing is delaying it, and that is done with water and airflow rather than chemicals. Keep the roots consistently moist, mulch, water at the base rather than over the leaves, and thin out crowded growth so air can move through the row. Rows planted too close together and shoots braided up a single strand of netting are the ones that go down first.
Remove the worst affected lower leaves as they appear rather than stripping the plant. Taking off a handful of gray leaves each week keeps air moving and slows the spread; taking off half the foliage at once weakens a plant that is already struggling.
When mildew has taken the row and the stems have gone short, clear it out. Pull the plants, take them off the netting, and put mildewed material in the rubbish rather than the compost. Then prepare the ground for the autumn sowing while you remember which end of the row went first.
Sweet pea seeds and pods are poisonous and are not related to the edible pea in any useful sense, despite looking very like it. Do not let anyone eat them, keep pods away from children, and do not grow sweet peas mixed into a row of edible peas where the two could be picked together by mistake.
Recording what went wrong and where
Note the date you first see aphids and the date you first see mildew. Both arrive at roughly the same point each year in a given garden, and knowing that date in advance turns a reaction into a plan: inspect for aphids a fortnight before they normally appear, and get the mulch and the watering right before mildew weather arrives.
Mark the position of any plant you pull for virus. If the same section of the row is affected two years running, the cause is usually a nearby overwintering host or a sheltered spot where aphids build up early, and the answer is to move the row rather than to change the seed.
Record losses at the seedling stage separately from losses later. Ten plants lost to slugs in the first week and ten lost to mildew in late summer are entirely different problems, and a single figure for the season hides both.
Note where the row was each year. Sweet peas do better on ground that has not grown them or other legumes recently, and a simple sketch of which bed was used each season prevents the slow decline that comes from repeating the same spot indefinitely.