Chislett Developments

M7 Orchard Protocol

Introduction

The M7 is a very early maturing navel orange which consequently has a shorter time for fruit growth between flowering and harvest, than later varieties. There is also a propensity for the variety to set heavy crops that can impact negatively on fruit size.

The variety is precocious and young trees can set heavy crops during a time where we seek to maximise tree growth and we don’t want to encourage alternate bearing, so it may be necessary to implement crop regulating practices earlier than would otherwise be required on other young navels.
To maximise profits fruit size has to be optimised. It is necessary therefore to ensure all possible cultural practices are followed to achieve this result.

The high vigour of the M7 can cause occasional bark cracking (Figures 1 and 2) which under normal circumstances heals without causing problems. Under particularly vigorous growing conditions and high humidity, these cracks can be more pronounced and the bark can turn a reddish-brown colour and occasionally can become infected by fungal or bacterial agents causing shoot dieback and bark damage. This high vigour also means that copper is readily depleted in the tree’s system. It is therefore very important to follow the recommendations for copper sprays below.

Using appropriate cultural practices the M7 has proven to be highly productive of excellent quality fruit.

Figure 1: Cracks which have healed on maturing wood

Figure 1: Cracks which have healed on maturing wood

Figure 2:  Reddish-brown colourisation of healed cracks

Figure 2: Reddish-brown colourisation of healed cracks

Figure 3: Vigorous three year old M7 tree

Figure 3: Vigorous three year old M7 tree

Young Tree Foliar Sprays

For the first two years after planting or top-working trees, it is recommended that foliar nutrient applications be used to maximise growth. 
Nitrogen, magnesium and trace elements should be used along with amino acids and other growth stimulants.
A low rate of copper should be mixed with every spray (e.g. 25 mg/100ml of copper oxide).
There should be good control of aphids and leaf miner by using an IPM strategy.

Trunk Guards on Young Trees

Trunk guards if too tight or do not have enough ventilation, can cause phytophthora infection of the bark under the guard. Guards must be removed as soon as they are no longer required for protection from herbicides.

Winter GA

Applications of winter GA will help in thinning flowers and reducing bunches of fruit and improving overall fruit size.

This practice should be applied starting the first winter after planting or top-working  in order to have balanced consistent crops.
Timing: Early June (in the Sunraysia region of Australia)
Rate: 10 ppm.
A second application at 10 ppm could follow at bud break (late July in the Sunraysia region) if a very heavy bloom (light crops on the tree, vigorous foliage and cold winters) is anticipated.

Pruning

The M7 has the tendency to grow thick canopies in the lower part of the tree leaving several layers of fruit that may not be of marketable size.
It is recommended that these layers be thinned by hand pruning removing medium sized limbs.  Annual pruning should always be considered to enhance fruit size.
The upper part of the canopy tends to be more open, setting less fruit that tends to be larger; therefore it will not be so critical to prune this part of the canopy.

      Top Worked trees – Different Technique Required

Top worked trees have been found to produce multiple, dense branches which because of the very vigorous growth tends to be long and whippy. This type of structure causes many fruit to be produced a long distance from a strong branch and this fruit is usually small.
Therefore in addition to the technique used on maiden trees, these long, whippy branches need to be removed or thinned out and their length reduced.

Crop Density 

It is important to have a balanced crop density and to measure it regularly every season to maintain the best yields, size and quality.
The optimum count frame is 4 to 5 fruits per frame (0.5 x 0.5 x0.5 m). If density is significantly higher, it will be important to remove some of the fruitlets by direct hand pruning. This should be done as soon as possible after physiological fruit drop.

Foliar Sprays: Potassium Nitrate

Regular foliar sprays with potassium nitrate will enhance fruit size development.
It is particularly important to apply potassium nitrate at the end of fruit set (early November in the Sunraysia region) around the same time as the fruit size enhancing spray (2,4-DPp Corasil).
A regular application of potassium nitrate at 2% during summer is recommended when crops are heavy.

Foliar spray: Fruit Size Enhancing Spray (2,4-DPp Corasil)

If a heavy fruit set is anticipated then an early Corasil spray when fruitlets are approximately 12mm in average diameter will assist in removing the small fruit from the tree. If the anticipated fruit set is moderate, then spray when fruitlets are larger (18 – 20 mm). Refer to the product label.
The effect on fruit quality will be minimal and should increase fruit size by up to one count.

Foliar Spray: Copper

As mentioned, the M7 is very vigorous and can quickly become deficient in micro nutrients, particularly copper. Regular applications of copper will reduce this incidence and will not have any commercial impact on production and quality.
Any high grade copper at 25% of the label rate could be added at every foliar spray.

Nutrition: Fertigation

The most important demand for nutrition is during the spring flush, fruit set and cell division.
In general, M7 compared with other navel varieties will require an increase in the fertiliser rates during spring flush (September – October) by 50% and during cell division (November – December) by 50%. Fruit quality should be monitored in case this strategy needs adjustment.
The fertiliser program should be completed by early February to allow the fruit rinds to smooth out.
For a normal cropping situation, the fertiliser program should be around 100-120 units of N, 30-45 units of P and 120-150 units of K.
Following very heavy crops, an N-P-K post-harvest fertiliser application of 10 to 25 units of N, P and K is recommended.

Indicative fertigation nutrient application program:

  N K
 Sep 20% 10%
 Oct 30% 10%
 Nov 15% 15%
 Dec 15% 15%
 Jan 10% 25%
 Feb 10% 25%
 TOTAL  100% 100%

 

 

 

Others: Flower Pruning, Hand Thinning

If at flowering time, there is a very heavy bloom, it may be advisable to prune lightly (by cutting only small flowering branches) to thin out part of the bloom.
If at the end of fruit set (early January) there are excessive fruitlets, some pruning directed to thin the excessive crop may be advisable.
If despite best practice, there is still an excessive crop in late January; consideration could be given to some hand thinning to remove the smallest fruit. This however, along with pruning at the end of fruit drop, should not be necessary if the above procedures are followed.

Disclaimer: Information in this document is provided as a guide and is of a general nature only. The information is subject to change by Chislett Developments Pty Ltd at any time without notice. The information is not to be relied upon as being complete, accurate or up to date or to serve as the sole basis of citrus orchard management. Primary references and full citrus orchard management principles, including labels and application instructions for fertilisers, sprays and chemicals, should be consulted.
Subject to any terms which cannot be excluded at law, Chislett Developments Pty Ltd accepts no responsibility for any loss, damage, cost or expense (direct or indirect) incurred by or as a result of any error, omission or misrepresentation in any information in this document. Growers are advised to always complete and assess a small trial before undertaking commercial scale applications.

Web strategy and design by LCUBED