Posts Tagged: replant

After a Fire, Replant or Topwork?

After the fires, the question has come up of whether an orchard should be replanted or topworked in the field, possibly to a new variety.  This has been an issue in the past and was addressed in a little study nearly 20 years ago. The study still bears relevance today and applies to both avocado and citrus.  The availability of avocado trees for replanting is in serious short supply, so replanting may not be an option at this point. 

There are many changes going on in the citrus industry and one opportunity is the conversion of an orchard to another variety of citrus. If this is a consideration, then the question becomes one of whether the orchard should be topworked or replanted with new nursery trees. If the trees are healthy and under 20 years of age (it is possible to topwork older trees) and the new scion is compatible with the interstock or rootstock, then topworking can come into production sooner than a new replant. If the planting density needs to be changed or serious soil preparation or a new irrigation system needs to be installed, then replanting might be the preferred choice.

The chance to convert is also dependent on the availability of new trees and budwood. New varieties can often be in short supply. It's best to make sure that for either option that the material is there. For topworking, T-budding is more conservative of material than stick grafting. If topworking is chosen, then it must be decided whether to graft the scaffold branches or the stump. Stump grafting makes for a lower tree, but scaffold grafting reduces the risk of losing the topworked tree from damage to the graft from birds, pests, wind or frost.

It is often assumed that topworking is cheaper than replanting, but as the following example shows, it probably is not. In Santa Paula, ‘Olinda' Valencias on ‘Carrizo' rootstock were converted to scions ‘Allen' Eureka lemon, or ‘Powell' late navel. In 1998 and 2000, the ‘Olinda's were interplanted with either ‘Allen' on ‘Macrophylla' or late navel ‘Powell' or ‘Chislett' (on either ‘Carrizo or ‘C-35' rootstocks). The ‘Olinda's were topworked in 2002 and 2003 to one of the new scions. In a few cases, ‘Allen' was stump grafted, but most trees were scaffold grafted.

Several steps are required for topworking that will ensure success. These are listed below:

• Get a reputable person to do the work.

• Time of year is critical for grafting. Spring is best.

• Leave a nurse limb.

• Decide to stump or scaffold graft.

o Stump grafting requires only 3 – 4 buds or sticks

o Scaffold grafting requires 2 buds per scaffold. Consider winds since even one-year old unions are very tender.

• Sequence of events

o Line up budwood

o Remove top of tree and stack brush

o Whitewash trunks

o Paint cutoff surfaces

o Insert grafts

o Wrap grafts with plastic tape

o Place white paper bag over grafts and tape in place

Later

o Keep after ants and snails

o Shred brush

o Remove bags when shoots start growing through them.

o Bi-monthly, in first year, brush out water sprouts. Less often in the next 2 years

Much of this work can be contracted with the grafter, who usually assures some level of performance, something like 90% take. It is up to the grower to ensure that pests do not take out the grafts.

The costs of topworking are associated with the costs of the budwood (as much as $3 per tree), the act of grafting (depending on stump or scaffold, $8-10 per tree) and water sprout removal. Sprout removal is six times in year one, eight times in year two and only four times in year three. At a labor rate of $12 per hour, sprout removal costs $7.20 per tree.

A like for like comparison of topworking versus replanting based on 2002 data is shown below.

So in the case of both the lemon and navels it costs a bit more to topwork, but the results are earlier production. Here the topworked trees gain the economic advantage. For example, if cultural costs were $1000 per acre per year (20 by 20 ft. spacing) and, conservatively, two years are saved, the maintenance savings per tree would be $18. In the above study the time advantage appears even greater. Three-year old topworked lemons produce about the same as 6-year old replants. Two year old topworked navels have a significantly larger canopy than six-year old replant navels and appear to have about the same fruit set for the coming year.

young avocacdo tree

One Symptom, Many Causes

We are creatures of habit and when we see the effects of a treatment, we can often persist in seeing the same or similar symptoms and assuming the cause is the same. In a recent case, a newly planted ‘Pixie' orchard, planted in August had gone into an old ‘Valencia' ground. The trees went through an adjustment period, but still didn't look sprightly in the fall. The grower applied a hand application of urea on the rootball that within 10 days had caused the trees to go into a salt swoon. Meaning, they got too much fertilizer that burned them. The grower seeing the effect, immediately started the sprinklers, but the damage was done. Several months later the trees had either died or were still lingering, but hanging in there. The trees were still coming out of winter, but the trees hadn't perked up. It was a dry winter and some of the yellowing was due to underirrigation, that overall yellowing from lack of nitrogen and the leaves were curled. But the assumption was still that the trees were recovering from the salt burn from the urea.

Looking more closely at the trees, something else was odd about some of the trees that were continuing to die. The leaves suddenly wilted. Getting down on hands and knees and digging around the roots, there were few roots and ………………………….a tunnel. A gopher had been at this tree and the lack of roots were probably due to Phytophthora root rot. Looking around there were some old ‘Valencias' that had been hit by gophers and there were gophers mounds and runs all over the place.

So, young trees planted in the heat of the summer into root rot ground with gophers waiting in anticipation that had been salt burned in a year with little rainfall.   A lot of causes for trees that generally weren't happy – triste, as they say in French.

So what are the lessons here? Avoid old citrus ground when planting with citrus, and if you can't make sure, don't plant in a stressful period. Phytophthora loves stressed trees and adding lack of rainfall an gophers and salt, just heightens the stress.  Make sure to get the irrigation right.  Don't irrigate them to the schedule of the older trees and start them off on one of the phosphite materials.

 

Images                      

Wilted, yellow leaves from lack of water and Phytophthora 

Gopher chewing on stem

Gopher run and lack of roots from Phytopthora and gopher

Gopher mounds in planting area

Older Valencias dead and dying from Phytophthora and gophers

citrus stressed

gopher damage2

gopher hole

gopher mounds

citrus gopher damage

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