Tony Dick­er­son answers your ques­tions

Garden News (UK) - - News - TONY DICK­ER­SON

Q What’s the best way to keep black spot on my roses un­der con­trol? Janet Fisher, Wragby, Lin­colnshire

A Black spot is a fun­gal dis­ease of roses where pur­ple or black spots de­velop on the leaves. The dam­age can be quite lim­ited, but in many cases the patches spread out­wards and much of the rest of the leaf turns yel­low be­fore drop­ping. It’s the most com­mon dis­ease of roses and can oc­cur from spring on­wards. Where just the odd leaf is in­fected you can just pick it off and bin it. But where roses are badly in­fected you need to take steps to re­duce the dis­ease, as the vigour of the plant will be af­fected if too many leaves fall. Older, species types of roses of­ten show good re­sis­tance, but black spot is a dis­ease that de­vel­ops new strains rapidly so even mod­ern roses sold as black spot-re­sis­tant may be­come in­fected af­ter two or three years. Drier sum­mers re­stricts the spread of the dis­ease, par­tic­u­larly in south­ern Bri­tain. The fun­gus spends the win­ter as rest­ing spores on fallen leaves, so col­lect­ing and de­stroy­ing fallen leaves in au­tumn will help pre­vent the spread. Also check for, and prune out, any stem le­sions in spring and don’t com­post prun­ings. Most fungi­cides avail­able to the home gar­dener will help con­trol the prob­lem, to­gether with other com­mon rose dis­eases such as rose rust and pow­dery mildew. It’s prob­a­bly not worth spray­ing now so late in the sea­son, but next year you should spray sus­cep­ti­ble roses on a reg­u­lar ba­sis fol­low­ing the man­u­fac­turer’s in­struc­tions.

There’s also a range of prod­ucts for roses that com­bine a fungi­cide and in­sec­ti­cide, but only con­sider us­ing th­ese if pests are ac­tu­ally present on the roses to avoid harm to ben­e­fi­cial pol­li­nat­ing in­sects. Pop­u­lar brands in­clude Bayer Mul­tirose 2 and Scotts Rose Clear Ul­tra. Th­ese will also con­trol com­mon rose pests, such as aphids and sawfly.

Most roses are best pruned in late Fe­bru­ary. Fol­low this up with an ap­pli­ca­tion of a rose fer­tiliser. If pos­si­ble, mulch round plants with well-rot­ted, farm­yard ma­nure or gar­den com­post. Re­peat the ap­pli­ca­tion of fer­tiliser in late May or early June.

If you don’t catch black spot early, plant vigour can suf­fer

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Spray roses dur­ing the grow­ing sea­son to pre­vent black spot

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