Rose bushes (Rosa) are quite robust plants and if you offer them good growing conditions, that is, well-drained soil rich in nutrients, good sun, and good aeration, you limit the risk of insect attack and the development of diseases. However, you won’t be sure because growing conditions, climate, and rose variety also play a role.
Fungal diseases of roses
Cryptogamic diseases of roses are fungal diseases, that is, those due to fungi that multiply as soon as humidity is high. The most suitable treatment for these diseases is Bordeaux mixture and horsetail manure.
Black spot disease
Black spots appear on the leaves, causing them to turn yellow and fall. The rainy periods of spring and autumn are conducive to this development, which contaminates neighboring rose bushes. Pick up fallen leaves and remove affected leaves.
Powdery mildew or “white rose”
A thin, white, floury layer covers the young shoots and shoots that braid as they curl, without the leaves falling. Humidity, especially from April to June and from September to November, favors its development. In prevention, avoid overwatering, and place the rose bush more in the sun. Remove affected parts. Spray a mixture of milk and water (1/10) on the rose and renew every 5 days until it disappears.
Botrytis
The branches and stems of the rot are gray with grayish mold, while the petals have white spots (or red on white roses). Rainy periods are favorable to this disease. Remove wilted flowers and affected parts.
mold
Yellow spots appear on the leaves, causing them to darken and then fall. It is still the rainy seasons that offer an ideal terrain for the development of this disease. Affected parts must be removed.
pink canker
The twigs dry out after bacteria have contaminated them through the waist wounds or graft scar. Rain favors the expansion of these bacteria. The affected parts should be removed and sprayed with the Bordeaux mixture.
Necklace Galle
If your rose bush loses its vigor, growths may have developed on the roots and neck to grab the rose sap. Planting periods are crucial: ensure the health of the roots and collar of the rose bush you buy because there is no treatment against this gall.
Insect attacks on rose bushes
If you observe your roses to admire or feel them, you will notice the presence of insect pests, if necessary because the attacks are often massive.
Black or green aphids
They colonize thorns, young shoots, leaves (including the underside) and suck the sap leaving behind a mold that will cause mold to form. Nettle manure and ladybugs are effective but spray especially a black soap solution, renewing every 3 days if necessary.
mealybugs
They form whitish clusters and, like aphids, they suck the sap and make the pieces they have traveled sticky, which also carries the risk of developing mold. To treat, spray nettle manure or a black soap solution to which you have added 1 teaspoon of vegetable oil and as much as 90° alcohol per liter.
Otiorhynchs or Rosebush Weevils
The eggs of these insects are deposited by the females in the young shoots that end up withering, especially when these insects multiply very quickly. Remove claw-covered parts or sunken buds, and tap the stem of the rose bush where weevils hide during the day. Otherwise, use a natural pyrethrin insecticide.
Caterpillars (moths, moths)
They are green, they hide at the bottom of the leaves that they devour. They then turn into brown caterpillars that hide underground at the foot of the rose bush during the day and continue to nibble on the leaves during the day. Step by step to catch and remove brown caterpillars, and if not, spray the Thuringian bacillus (Bacillus thuringiensis), but it only acts on young caterpillars. Use the repellent effect of tansy by placing twigs at the foot of the rose: it will be an advantage.
sawflies
These small defoliator wasps are false caterpillars, they are also on the stems and then the larvae eat the leaves leaving only the veins. Remove all infested, bitten, or egg-containing pieces and crush well. A pyrethrum insecticide will be the only way to overcome it.
Yellow mite or red spider
Often called false red spiders: they are so small that we notice them, in summer, always too late, when they have already managed to form small thin canvases, with white dots on the leaflets, which shows that they suck sap. Spray a decoction of garlic that has acaricidal properties.
