Tag Archives: thrips

The October Garden

The glory of the sino nuttallii rhododendrons

The glory of the sino nuttallii rhododendrons

Floral Legacy in bud

Floral Legacy in bud

Rhododendons may no longer be the elite fashion item they were for so many decades, but we still love them.

When we started in the plant business back in the early 80s, rhododendrons were a hot ticket item. We were but one of several rhododendron nurseries in Taranaki and to survive, we needed to find our own niche. To this end, we grew a different range, specialising in varieties that would perform well in warmer climates – like Auckland. After all, even back then, one in four New Zealanders lived in greater Auckland and we figured that if we were going to sell them rhododendrons, we might as well sell them ones that would do better for them. Mark’s father just happened to have done some breeding to find varieties that were more resistant to thrips, didn’t get that burned and crispy edging to their foliage and were predominantly fragrant as well as floriferous. It gave us a good place to start.

Nowadays there are no specialist rhododendron growers in Taranaki at all and the demand has melted away. I no longer have to try and convince people that not all rhododendrons have a big full truss in the shape of a ball but many have loose trumpets in curtains of bloom instead.

Rhododendrons are one of the backbones of our garden and we wouldn’t have it any other way. While they have a relatively short season in full bloom, the anticipation of fattening buds stretches out the weeks with the promise of delights to come. They are as fine a shrub as any we grow here and a great deal more spectacular than most.

The nuttalliis! Oh the nuttalliis!

The nuttalliis! Oh the nuttalliis!

The nuttalliis. Oh the nuttalliis. Peak nuttallii season doesn’t start until closer to the end of the month, taking us into November but some varieties have already done their dash for this year. If we could grow only one type of rhododendron, we’d choose a nuttallii and even more specifically, the sino nuttallii from China. You can keep your big red rhodos (most people’s favourite pick). We love the fragrant, long, white trumpets which look as if they are made from waxed fabric, the lovely peeling bark and the heavy textured foliage. These are rarely offered commercially now so grab one if you ever find it for sale.

Thrips!

Thrips!

It is, by the way, nasty little leaf-sucking thrips that turn foliage silver and no, you can never turn those silver leaves green again. If you look at the underside of the leaf, you can see dark thread-like marks – these are the critters that do the damage. All you can do is to try and prevent the new season’s growth from getting similarly infested. We are not at all keen on spraying insecticide these days and you need a systemic insecticide that the plant absorbs into its system to get a thorough kill. If you must go down this path, spray in mid November, early January and late February for maximum effect. Others praise Neem oil instead but we haven’t tried it.

We favour choosing more thrip-resistant varieties, keeping them growing strongly and opening up around them to let more air and light in. Thrips prefer shade and shelter. Unless it is really
special, if it is badly thrip-prone, we replace it with a better variety. Not every plant is precious.

In the longer term, plants come and go in the fashion stakes. Goodness, even red hot pokers are having a resurgence of popularity. We don’t worry about the fashion status of the rhododendron and Mark continues hybridising for better performing cultivars. If there is no commercial market for the results, it doesn’t matter. We will continue to enjoy them in our own garden.

First published in the New Zealand Gardener and reprinted here with their permission.

Rhododendron Barbara Jury - one of Felix's  hybrids

Rhododendron Barbara Jury – one of Felix’s hybrids

Garden lore

“I am very fond of the Spring-flowering colchicums, but unfortunately slugs are also, and those greedy gastropods and I have a race for who can see the flower-buds first. If I win I go out after dark with an acetylene lamp and a hatpin and spear the little army of slugs making for a tea-party at the sign of the Colchicum.”

Edward Augustus Bowles My Garden in Spring (1914)

Thrip infested leaves to the left, healthy to the right.

Thrip infested leaves to the left, healthy to the right.

Thrips galore

Clearly last summer’s drought stressed some plants more than we realised at the time. Thrips. We have thrip infestations on plants which do not normally suffer. Plants show the damage as silvering on the leaves. It is common in many rhododendrons but bay trees and photinia are also prone to infestations, along with other plants. You can’t turn the silver leaves green again. Turn over the leaf and you will see rusty looking spots behind. This is the residue of the thread-like thrips which suck the chlorophyll out of the foliage. The damage is done.

Prevention is better than a cure. A strong, healthy plant with plenty of air movement around it and good light levels is better able to withstand attack. There are systemic insecticides you can use which the plant absorbs into its system, killing the thrips from the inside out but you have to wait until the critters are active again – usually late November. The bands sold that you wrap around the trunk of the tree will either be soaked in systemic insecticide or in Neem oil. We have never tried Neem and are surprised if it works as a systemic, but others say it does.

Contact insecticides don’t work unless you can saturate the underside of every single leaf so most organic remedies won’t work. The fresh spring growth will hide a multitude of sins and we are hoping that the thrippy plants will look fine again. Some varieties are much worse affected and generally we choose to remove those and replace with better performing varieties because we do not want to have to use systemic insecticides just to keep plants healthy.

First published in the Waikato Times and reprinted here with their permission.

In the Garden this week: Friday December 24, 2010

• Dear Santa, thank you for the pre-Christmas gift of rain. But enough is enough. Water tanks are overflowing, the grass is growing again and we really could do with a return to sunshine and warmer temperatures for the Christmas and New Year break.

• Watch for an explosion of fungal ailments in the humid conditions, especially on tomatoes, cucurbits and potatoes. Roses will also suffer but they can grow out of it whereas vegetables can succumb entirely. It will almost certainly be necessary to get a copper spray on when the weather dries out. If you would rather try baking soda, a level teaspoon per litre is the recommended dose. The big problem with baking soda is that you have to spray a great deal more frequently – probably weekly.

• The wet weather means that you can still lift and divide many clumping perennials even now. Most of them are in full growth, so as long as you make sure they don’t dry out, they will recover quickly. Replant into well cultivated, tilled soil enriched with compost.

• Grapes need thinning out. We keep to one bunch per side branch. More is not better and you can over crop grapes, leading to inferior fruit. Trim back laterals. If they get too heavy, they can break away too easily and you will lose your bunches of fruit. You also want the plant to concentrate its energy on the fruit, rather than the excessive leafy growth.

• If you have not mulched your garden beds and were alarmed at the recent dry spell, this week’s rain has probably raised the moisture levels sufficiently for you to get a layer of mulch on now. We much prefer vegetative mulches which break down and get incorporated into the soil over time – compost, leaf litter, bark or shredded wood waste and the like. Inert mulches like stones, gravel or lime chip do work to keep the soil moist and suppress weed seeds to some extent but they are not suitable for gardens that you want to dig over or replant at any time and they certainly do nothing to add nutrients or texture to the soils. They are best for areas you don’t actually garden and even then, they are a bit of a mission to keep clean unless you have a handy blower vac.

• Keep up with deadheading (basically anything that has finished flowering) and try and stay on top of the weeds which will have been triggered into rapid germination and growth by the rains.

• If you had a problem with silver leaves on rhododendrons last year and haven’t sprayed this spring, check underneath the leaves for something that looks like dirty threads. These are the thrips which suck the chlorophyll out of the leaves. Photinia and honeysuckle both harbour thrips too. If you are going to spray, it needs to be a systemic insecticide so the plant sucks it into its system (as opposed to a contact one which only kills insects where it touches). Bands soaked in neem oil secured around the trunk are getting good reports. If you want to make your own, soak a strip of old woollen carpet in neem and then secure it around the main stem with the carpet pile inwards. Thrips don’t usually go away of their own accord. You either need to change the growing conditions, kill the insects or remove the host plants altogether.

Outdoor Classroom – Rhododendrons: common problems and solutions

1) Silver leaves. By far the most common problem is thrips sucking the chlorophyll out of the leaves, turning them silver and weakening the plant. Turn the leaf over and you may find black, thread-like insects on the back. Replace heavily infested plants – some varieties are more susceptible than others. Open up around the plant for more air movement and light. You can use a systemic insecticide – spray November, early January and, for really bad cases, late February. Neem oil is recommended by some as an alternative to insecticides.

2) Leaves with dry brown patches and edges. This is usually a sign of stress. The plant may be too dry or too hot. Move it if necessary (sun for half the day or dappled light is best) and get a blanket of mulch over the roots. Some varieties prefer a much colder winter than we have and these tend to burn and crisp on the leaves. Replace them. Some plants get touched by mildew and lichen. Open up to allow more air movement.

3) No flower buds. This is usually a sign of too much shade. Move the plant or open up around it to allow more light.

4) Leggy, bare and stretched. Again, this is usually a sign of too much shade. Some varieties have a tendency to get rangy and open, others are naturally more compact and bushy. You can rejuvenate a leggy plant by cutting back very hard but it is really too late in the season now. It is best done in the middle of winter. You are more likely to kill the plant if you cut it back to bare wood now. This plant was cut back hard two months ago and has made its new growth already.

5) Plants which make only one new growth from each stem can be encouraged to make several growths by pinching out the single shoot. Do this as early as you can or you will be pinching out next year’s flower buds. In the right hand photo, you can see a plant making several new shoots instead of only one.

6) If not deadheaded, some rhododendrons set so much seed that it can weaken and even kill them. It can also reduce flowering the next season. This plant missed being deadheaded last year. Varieties that don’t set seed are generally deadheaded for aesthetic reasons, not because it is necessary.