The British Gladiolus Society

Pests and Diseases Part II

Gladiolus Rust Uromyces transversalisThümen

The Gladiolus rust , Uromyces transversalis is a disease of quarantine importance in Europe and the United States. Because it attacks mainly hybrid cultivars it would have serious consequences if it became established in greenhouses or nurseries. The sori or spore producing bodies are unusual as they develop across the width of the leaf rather than longitudinally along the veins as in most monocots.

Botrytis

This disease is usually associated with the later part of the season when days are still warm but nights are cool and there is a large amount of moisture in the atmosphere. It is usually compounded by a lack of air flow around the leaves of the plant, especially evident if planted too closely together. The symptoms are small brownish spots on the leaves which often merge to form larger areas which eventually may develop into a mouldy grey growth.

Virus

jpgThere are many virus diseases which may occur resulting in mottled, streaked or spotted leaves. The effects on the florets can be patches of colour that are different from the norm ie white or purplish. In some cases, corms may also be affected becoming shrivelled. Some viruses cause curling of poor small spikes, small corms and poor root development. Important to destroy such plants

Thrips Taeniothrips simplex

The thrip is potentially the worst pest to attack gladiolus - it can also attack other garden plants. It has the ability to severely damage a whole crop. The symptoms are not usually noticed until the infestation has occurred and by this time it is usually too late to rescue the situation. The one saving grace is that the insect cannot overwinter out of doors in northern Europe and northern North America. Plants severely infested with gladiolus thrips have a spotted, bleached appearance with silvery streaking between the leaf margins. Both leaves and petals act as a food source and will appear withered. If flower buds are seriously damaged, the flowers fail to open. The entire plant may become stunted. The eggs are opaque, white, kidney-shaped, and about 0.34 mm long and 0.2 mm in diameter. Gladiolus thrips emerge as creamy yellow larvae, but soon turn dark brown, except for the tips of the legs which are lighter. The wings are brown above and lighter below and appear to be darker with a grey band when folded over the back. Gladiolus thrips are about 1.5 mm long and extremely slim. Males are smaller and lighter in colour than the females. The life cycle of the thrip is very much determined by the weather and in warmer conditions several generations can be produced in a short time hence the apparent sudden epidemic.

Slugs And Snails

Both slugs and snails can cause damage but in most cases it is purely cosmetic, however a severe attack to the leaves can affect the plants ability to produce a new corm for the next season. Slugs have the potential to destroy the growing shoot of a newly planted corm but once established the plant should be safe from their clutches. Snails can affect the florets and make them unsuitable for exhibition.

And I Thought Thrips Were Bad

wireworms

2011 was going to be the year when I returned to the show bench with a vengeance, land availability has always been a problem in my area and for the past few years I have survived as a gladiolus grower by borrowing small pieces of land from the neighbours but not in 2011, oh no this year I had an allotment. Yes after pressure from a group of enthusiasts (after six months of waiting it has to be said some were more enthusiastic than others), the local council finally gave us a pasture field to use as allotments on the proviso that we fenced it off from local cattle and that it didn t cost them anything either financially or in resources. This was agreed and on March 1st my first ever allotment plot was allocated to me, this was quite early enough as until then the plot had been very wet and it wasn t fit to walk on. Time however was getting on and with a degree of urgency digging began to get the plot ready for April planting. Some plot holders took what I thought was the easy way out and removed the top three or four inches of turf and duly stacked it at the far end of their own little kingdoms but not me, no clever clogs here thought that as there was a lot of goodness in the top layer it would be best dug in so this was done and I waited patiently for any weeds to grow through so that I could eradicate them but the spring was very dry and hardly any appeared-this was as it turned out, the first sign that something may be amiss. Ahead of planting the soil was once more turned over and it seemed that all was well the soil was nice and friable, warm and still had a reasonable amount of moisture present, no stones and only the odd chafer grub. With everything set therefore planting began on April 27th starting off with a few late flowering cultivars, around fifty corms in all which were followed through to the end of May at regular intervals until a total of six hundred corms had been planted.



Wireworm Damage



By the time the last corms went in the first had begun to break through the surface and to say that they were sporadic would be an understatement. Growth was slow and I began to get a little concerned were the nutrients available to the plants or were they too dry The plants were watered and following a quick pH test carried out with a kit from a local hardware store which suggested that the soil was almost neutral, a nitrogen feed was applied to give them a bit of a boost-all to no avail. By now the next batch were coming through, again sporadically and the first batch were looking decidedly sorry for themselves. A leaf was examined and it came away in my hand and when the soil was excavated to find the corm it was obvious that the shoot had for some reason rotted away from the corm, but no sign of any culprits. Extensive research on the internet followed to try to ascertain a cause, could it be Sclerotinia A disease well known to be present in pasture land, could it be Botrytis after all a wet winter had been followed by a really dry spring-nothing seemed to really add up and all the time the later batches were following the same pattern as those planted earlier, in fact they were worse and those planted in mid May which sadly included the BGS trials hardly showed their heads above the ground. There was nothing for it drastic action had to be taken, firstly soil samples were gathered from around the plot and sent away for detailed analysis, secondly the soil was drenched with Jeyes fluid to try to kill off any pathogens and thirdly the decision was taken to pull up the few healthy looking plants from the first planting. It was this that gave the first indication of the cause for when the corms were lifted they were riddled with wireworms, little orange worms the larvae of the Click beetle. Again it was back to the internet to find a cure-sadly the only remedy Gamma BHC dust was withdrawn years ago, worse still the indications were that the lifecycle of the beastie would suggest problems for a few years to come. Looking into the conditions required by the wireworms damp winters, uncultivated land and deep rooted weeds on which to lay eggs, it would seem my plot was destined to be wireworm heaven and the final blow arrived a few days later when the soil sample came back with a pH of 5.4 suggesting my initial test had been quite inaccurate and sadly as the wireworms like acid soils it was perfect for them. So what could I do, faced with the loss of most of my glads I immediately volunteered to judge any shows that had not already allocated officials, as this would at least keep my interest levels high. On the allotment site I followed one of the pieces of advice found on the internet and began placing bait in the form of potatoes on the end of barbecue skewers all around the plot. The aim of these was to draw out as many larvae as possible and believe me it worked, the potatoes were checked every four or five days and the wireworms present were destroyed and gradually the numbers reduced. Hopefully the potatoes aligned to the fact that the adults had no vegetation onto which to lay a new batch of eggs may enable me to try again next season but a few bait stations will be tried out first. Interestingly enough those who skimmed their plots had no problems wonderful crops of potatoes and carrots but who know what is lurking in their piles off turf ready to inflict damage next year!

Nigel Coe





Wireworms Damage
Founded 1926