Rats in Fruit Trees

Hollowed out oranges, papaya, bananas and other fruits, whether hanging on the tree or on the ground, are definitely signs of rat feeding.  In Hawaii, there are four rodents that cause economic hardship: the roof or black rat, the Norway or brown rat, the Polynesian or Hawaiian rat, and the house or field mouse. In addition, they are carriers of contagious diseases including plague, murine typhus, leptospirosis, and salmonellosis. Today, most notably, they are part of the disease cycle known as Rat-Lungworm. See health.hawaii.gov/docd/disease_listing/rat-lungworm-angiostrongyliasis/  for more information and prevention of this serious condition.

Rodent control is not easy due to their ability to adapt to changes and their capacity to reproduce.

Rats are nocturnal. They have excellent memories and very repetitious habits. They are easily frightened of new things placed in their environment. The roof rat is most pronounced in this tendency. Rats have a keen sense of smell and hearing, and only a fair sense of sight with the ability to see in the dark.

Besides the hollowed out fruits, other common signs of rats are droppings, rubmarks, gnawings, nests, and unpleasant odors.  

                                                         Rat Damage on Oranges - UC IPM

In controlling these pests around the home, the first step is to clean up the environment by removing accesses to food and shelter. Physical barriers such as screens may need to be installed. When only a few rats are involved, trapping can be successful, both live and snap traps. Devices that kill rats by electrocution (e.g., Rat Zapper or Victor Electronic traps) are expensive but effective.

Paraffin-type bait blocks containing anticoagulants are also effective in controlling rats. They appeal to the rats gnawing instinct, especially those blocks with numerous ridges. Baits should be replaced immediately as they are eaten, since a single feeding on the first generation anticoagulants such as diphacinone, will not control rats; multiple doses over several successive days is required. The newer “second-generation” compounds such as brodifacoum, bromadiolone, difenacoum, and difethialone, which can be fatal after a single feeding. Prepackaged, ready-to-use bait stations containing some of these toxicants can be purchased by homeowners. 
   

Some poisons have a secondary effect which will affect animals that consume dead or nearly dead rodents. Thus, it is imperative that strict safety precautions be used in the placement and disposal of poison baits for rodents.

For more information on rats see the UC IPM website, http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74106.html

Dry, Flavorless Citrus?

Overly mature fruit is a major cause of dryness in citrus. In other words, if the fruit is left on the tree too long, drying occurs.  A few other reasons include:  1) the application of too much nitrogen.   2)  At times, dryness may occur when a tree is young; the fruit will improve as the tree ages.    3) Trees budded on certain vigorous rootstocks will make the problem of dry fruit worse. 4) For citrus grown in temperate climates, dry fruit is the result of low, freezing temperatures.   Overall, certain varieties of citrus, especially mandarins, seem to be more susceptible to producing dry fruit.  In Hawaii and other tropical areas, a further complication is the fact that citrus fruit does not color well. In other climates, such as California, fruit develops a deep orange color due to the great differences between day time and night time temperatures.  And under these conditions, oranges may actually turn color before they are sweet enough to pick.  In the tropics, however, where there are less temperature fluctuations, the orange coloration does not develop well and therefore is not a good indication of ripeness. In fact, fruit is often sweet but will still show a green coloration; by the time the fruit shows good color, it may have dry segments already forming.  If you don’t know the harvest season for your particular fruit, I would suggest picking one good sized fruit, even though it may still be greenish in color.  If it is not sweet enough, pick one every 1-3 weeks until it tastes sweet. Fruit will develop more sugar the longer it is held on the tree.

Sweetness in Citrus Fruit or Lack of It!

Warm sunny days: The accumulation of heat units is most important in determining the sugar content in citrus. Simply put, citrus fruits become sweeter the longer they remain on the tree up to a point. If the fruit seems ready to pick, but the taste is not sweet enough, then leaving it on the tree a little longer should sweeten it.   

Location, location, location: In certain places, fruit from a given tree will simply not produce enough sugars. Of the hundreds of citrus varieties, not all are adapted to a specific area. For a given region, some varieties won’t produce good quality fruit!

The rootstock factor -  There are numerous citrus rootstocks. They impart a variety of characteristics to the fruit. Some rootstocks will enable the tree to produce an abundance of fruit, but with poor quality, in this case, low sugar content. For commercial growers, choosing the right rootstock is an important factor when selecting new trees for an orchard. Homeowners on the other hand, have few choices in rootstocks when purchasing a tree.


  Will citrus fruit get sweeter by adding potassium or lime to the soil?

The notion of adding potassium or lime to sweeten citrus fruit has been around for a long time, but it has not been substantiated by scientific research. Fruit from trees deficient in potassium are small and thin-skinned, yet they can be juicy and have a good acid and sugar content. Adding potassium to deficient trees will increase the size of the fruit. This has also been noted in other fruit trees, such as apples and peaches.  An excess of potassium makes fruit large with coarse rinds, thick skins and poor eating quality.

 A classic chart taken from the University of California’s Citrus Industry Volume II, shows that as the percent of potassium in the leaf rises, there is a slight decrease in the sugar content of the juice in the fruit.  The vitamin C, however, content increases.

If soils are truly potassium deficient, by all means apply potassium. This being said, sweeter fruit will not be a result of adding potassium.

In regards to lime (calcium carbonate), an old study (1958) in South Africa, on calcium deficient orange trees, noted that the fruit was acidic and low in sugars. The trees were stunted, chlorotic (yellow), sparsely foliated and exhibited profuse blooming and excessive young fruit drop. If the soil is truly calcium deficient, adding lime may increase the sugar content of the fruit. A soil analysis can determine whether the soil is deficient in calcium, as well as other nutrients. Contact a local university cooperative extension to inquire about where an analysis is available.