All the information you need to handle petunia pests, diseases and other problems. How to quickly rid your plants of aphids and horn worms. Discover safe, effective, organic insect treatments.
In caring for petunias you may encounter a few petunia pests. Horn worms like to bore holes into newly formed flower buds and, to add insult to injury,they leave their black droppings all over the plant.
These are the same green caterpillars that invade your vegetable patch and make a buffet lunch of your tomatoes and sweet peppers. Their coloring makes them hard to spot amongst the leaves.
Bud worm caterpillars also eat petunias. They are green like the horn worms and may be treated in the same way.
If you only have a few of these petunia pests, you can hand pick them. Take a jar of soapy water into the garden with you and drop them into it. If there are lots of them, use BT.
Bacillus thuringiensis is an organic pesticide that will not harm people or pets but stops the worms from eating.
Other, less common petunia pests are aphids and cutworms. Cut worms are only a problem for new transplants. The wrap themselves around the main stem and cut it off, killing the plant.
You could place a toothpick next to each transplant’s stem to prevent this, but you probably don’t need to go to the trouble unless cutworms have been a problem for you in the past.
If you find seedlings cut off at the soil line, you have cutworms. Dig in the soil around the damaged plants, find and kill the worm. They are usually brown or black and curl into a ball when disturbed.
Aphids are usually yellow or green and tiny.
They congregate at the tips of new growth and on the undersides of the foliage. The aphid's MO is to attack plants weakened by drought stress or an overabundance of food and water.
A mild infestation will do no permanent harm. Adjust the plant’s culture and these petunia pests should go away.
If they increase in number, steps will have to be taken to eradicate them. Aphids can spread viruses among plants. The least toxic way to deal with these petunia pests is to subject them to a strong spay of water with the garden hose. This will knock them off the plant.
Most of them will die before they can climb back onto your petunias.
Lady Beetles and parasitic wasps are natural enemies of the aphid. If these good bugs are present in your garden, they will keep the aphid population in check as long as you don’t kill them with broad spectrum pesticides.
If nature is not getting the job done, you also have the option of purchasing these beneficial insects online and releasing them into your garden yourself.
Petunias are not particularly disease prone but here are two to watch for.
Damping off will sometimes cause petunia seeds to rot during germination or kill the new sprouts. You can prevent this by keeping seedlings warm and not too wet.
If your petunias develop stunted or deformed foliage or discolored, deformed flowers, they probably have a virus. Pull them out, bag and destroy them to keep nearby plants from becoming infected as well. There is no way to cure the virus once it has taken hold.
Find and destroy any aphids in the area.
Other petunia diseases include alternaria blight, crown rot, botrytis and fusarium wilt. You could spray your plants with a fungicide a few times per season to prevent these fungal diseases. I would only do this if I had had a problem with fungal diseases in the recent past. Healthy plants are not usually bothered.
Petunia hybrids can develop a few problems as the growing season wears on.
The most common problem is that they stop blooming.
This usually happens because the plants have not been pinched. Pinch off the dead blooms and your petunias should put out another flush of flowers.
Another reason for sparse bloom can be lack of fertilizer. How often have you been feeding the plants?
Feed them every other week with a water soluble plant food.
Another common petunia problem is that the large double petunia flowers will fall in the rain. This happens because petunia grandiflora has such big blooms that they become too heavy for the plant's stems when wet.
The only remedy for this is to grow the grandiflorias indoors and use the floribunda and multiflora types when you want to grow petunias in the ground.
Growing petunias indoors means keeping them in very bright light. A greenhouse or Florida room would be the best setting.
We earn a commission when you buy products via the links on this site. Without these sales, it would be impossible for us to keep botanical-journeys-plant-guides.com online.
Small donations are also gratefully accepted:
Thank you very much, we appreciate your support.
Your plant guides,
Selina and Tiny