Peter Cun­dall:

Plant growth, flow­er­ing and fruit­ing can be af­fected by mildew in­fec­tions but some sim­ple steps help to over­come the prob­lem, writes PETER CUN­DALL

Sunday Tasmanian - Tassie Living - - TASSIE LIVING -

Plant proteas to add colour in win­ter.

For­tu­nately when mildew strikes late in the sea­son, lit­tle dam­age will oc­cur

MILDEW prob­lems on plants seem to get worse in au­tumn, al­though they can strike at any time dur­ing the grow­ing sea­son. Mostly they ap­pear as in­signif­i­cant dots or blem­ishes on young or old fo­liage then spread rapidly.

For­tu­nately when mildew strikes late in the sea­son, lit­tle dam­age will oc­cur. The worst mildew prob­lems oc­cur in spring or early sum­mer. This is when vigour, flow­er­ing and fruit­ing are se­ri­ously re­tarded by this dis­ease.

Ba­si­cally, there are two main mildew groups. Pow­dery mildew and downy mildew look dif­fer­ent from each other so are eas­ily iden­ti­fied.

Pow­dery mildew looks like white or pale grey ash cov­er­ing young leaves, green stems and oc­ca­sion­ally fruit, and can strike any time dur­ing ac­tive plant growth.

This mildew usu­ally sur­vives win­ter. Dur­ing late win­ter the youngest shoots of vul­ner­a­ble ap­ple va­ri­eties such as Jonathan of­ten show signs of where the dis­ease has over-win­tered in in­fected shoots, which have a thin, shrunken ap­pear­ance.

In spring the first leaves are im­me­di­ately cov­ered with pow­dery mildew and shrivel within days.

If not treated, the dis­ease per­sists through­out sum­mer and au­tumn, weak­en­ing trees and mas­sively re­duc­ing ap­ple yields. The treat­ment is to cut off all in­fected shoots, col­lect­ing all in­fected ma­te­rial in a wheel­bar­row so it can be carted away.

Other forms of pow­dery mildew oc­cur on late-sown peas as leaves and pods be­come white with the pow­der. The dis­ease usu­ally strikes pea plants which are over­crowded, as tem­per­a­tures rise in sum­mer. Luck­ily the peas within in­fected pods are per­fectly dis­ease free and ed­i­ble so there is lit­tle point in spray­ing. Bet­ter to sow pea seeds in Au­gust, so har­vest­ing can be­gin in De­cem­ber.

Or­na­men­tal plants which be­come eas­ily in­fected with pow­dery mildew in­clude semi-ev­er­green rose va­ri­eties such as the com­mon Banksia rose. It is the leaves on tan­gled growth which come un­der pow­dery mildew at­tack, even worse if roses are in too much shade.

Prun­ing and thin­ning con­gested growth gives ex­cel­lent con­trol. It is best car­ried out in early Jan­uary but any time of the year gets good re­sults. Dras­ti­cally thin­ning, re­ar­rang­ing and spread­ing branches to al­low air to move freely through plants makes con­di­tions dif­fi­cult for pow­dery mildew.

Right now in many au­tumn veg­etable gar­dens, pow­dery mildew has al­ready started to show up on parsnip, cucumber, pump­kin and zuc­chini leaves. Parsnips sown in mid-spring will have roots big enough to eat. So do noth­ing. Just leave parsnips in the ground un­til they have been sweet­ened by frosts, then en­joy them through win­ter and spring.

Younger, smaller parsnips can be sprayed with a so­lu­tion of one part of milk to 10 parts of wa­ter to pro­vide good con­trol.

Many pump­kin and espe­cially zuc­chini leaves are al­ready show­ing signs of mildew in­fec­tion. This is no big deal. It usu­ally hap­pens as the plants age and ma­ture, just as we get grey­ing hair as we get older. With zuc­chini plants, the first leaves to be at­tacked are older, lower leaves. Cut them off at the first signs of mildew in­fec­tion and this pro­longs the life and fruit­ing of the plants.

Downy mildew is a dif­fer­ent type of fun­gal dis­ease. It at­tacks leaves of grapes, cu­cum­bers, bras­si­cas, let­tuce, onion, pan­sies and even beet­root. Dark, slightly sunken patches ap­pear on the up­per sur­faces of leaves. On the un­der­sides, clus­ters of glis­ten­ing pur­plish or sil­very down ap­pear.

Spray­ing grapevines with Bordeaux or Bur­gundy mix­tures as a pre­ven­ta­tive cover has been fairly suc­cess­ful over many years.

Open­ing up plants to lots of free air cir­cu­la­tion also helps stop mildew from tak­ing hold. A sim­ple, safe means of con­trol is to dis­solve two tea­spoons of bi­car­bon­ate of soda in a litre of wa­ter, add a drop of house­hold de­ter­gent and spray at the first signs of in­fec­tion.

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